trong từng hạng tử.
< / d i v > < p > − < s t r o n g > C a ˊ c h g h i n h ớ h i ệ u q u ả : < / s t r o n g > H a ~ y n h ớđ u ˊ n g t h ứ t ự d a ^ ˊ u “ + , − , + , − ” v a ˋ l ư u y ˊ h ệ s o ^ ˊ 1 − 3 − 3 − 1 k e ˋ m t h e o l u ~ y t h ừ a g i ả m d a ^ ˋ n c ủ a < s p a n c l a s s = " m a t h − i n l i n e " > < s p a n c l a s s = " k a t e x " > < s p a n c l a s s = " k a t e x − m a t h m l " > < m a t h x m l n s = " h t t p : / / w w w . w 3. o r g / 1998 / M a t h / M a t h M L " > < s e m a n t i c s > < m r o w > < m i > a < / m i > < / m r o w > < a n n o t a t i o n e n c o d i n g = " a p p l i c a t i o n / x − t e x " > a < / a n n o t a t i o n > < / s e m a n t i c s > < / m a t h > < / s p a n > < s p a n c l a s s = " k a t e x − h t m l " a r i a − h i d d e n = " t r u e " > < s p a n c l a s s = " b a s e " > < s p a n c l a s s = " s t r u t " s t y l e = " h e i g h t : 0.4306 e m ; " > < / s p a n > < s p a n c l a s s = " m o r d m a t h n o r m a l " > a < / s p a n > < / s p a n > < / s p a n > < / s p a n > < / s p a n > v a ˋ t a ˘ n g d a ^ ˋ n c ủ a < s p a n c l a s s = " m a t h − i n l i n e " > < s p a n c l a s s = " k a t e x " > < s p a n c l a s s = " k a t e x − m a t h m l " > < m a t h x m l n s = " h t t p : / / w w w . w 3. o r g / 1998 / M a t h / M a t h M L " > < s e m a n t i c s > < m r o w > < m i > b < / m i > < / m r o w > < a n n o t a t i o n e n c o d i n g = " a p p l i c a t i o n / x − t e x " > b < / a n n o t a t i o n > < / s e m a n t i c s > < / m a t h > < / s p a n > < s p a n c l a s s = " k a t e x − h t m l " a r i a − h i d d e n = " t r u e " > < s p a n c l a s s = " b a s e " > < s p a n c l a s s = " s t r u t " s t y l e = " h e i g h t : 0.6944 e m ; " > < / s p a n > < s p a n c l a s s = " m o r d m a t h n o r m a l " > b < / s p a n > < / s p a n > < / s p a n > < / s p a n > < / s p a n > t r o n g t ừ n g h ạ n g t ử . < ! − − L A T E X P R O C E S S E D 1 756993854712 − − > < / p > < p > − Đ i e ^ ˋ u k i ệ n s ử d ụ n g : C h ỉ s ử d ụ n g k h i h i ệ u ở c u ˋ n g d ạ n g < s p a n c l a s s = " m a t h − i n l i n e " > < s p a n c l a s s = " k a t e x " > < s p a n c l a s s = " k a t e x − m a t h m l " > < m a t h x m l n s = " h t t p : / / w w w . w 3. o r g / 1998 / M a t h / M a t h M L " > < s e m a n t i c s > < m r o w > < m o s t r e t c h y = " f a l s e " > ( < / m o > < m i > a < / m i > < m o > − < / m o > < m i > b < / m i > < m s u p > < m o s t r e t c h y = " f a l s e " > ) < / m o > < m n > 3 < / m n > < / m s u p > < / m r o w > < a n n o t a t i o n e n c o d i n g = " a p p l i c a t i o n / x − t e x " > ( a − b ) 3 < / a n n o t a t i o n > < / s e m a n t i c s > < / m a t h > < / s p a n > < s p a n c l a s s = " k a t e x − h t m l " a r i a − h i d d e n = " t r u e " > < s p a n c l a s s = " b a s e " > < s p a n c l a s s = " s t r u t " s t y l e = " h e i g h t : 1 e m ; v e r t i c a l − a l i g n : − 0.25 e m ; " > < / s p a n > < s p a n c l a s s = " m o p e n " > ( < / s p a n > < s p a n c l a s s = " m o r d m a t h n o r m a l " > a < / s p a n > < s p a n c l a s s = " m s p a c e " s t y l e = " m a r g i n − r i g h t : 0.2222 e m ; " > < / s p a n > < s p a n c l a s s = " m b i n " > − < / s p a n > < s p a n c l a s s = " m s p a c e " s t y l e = " m a r g i n − r i g h t : 0.2222 e m ; " > < / s p a n > < / s p a n > < s p a n c l a s s = " b a s e " > < s p a n c l a s s = " s t r u t " s t y l e = " h e i g h t : 1.0641 e m ; v e r t i c a l − a l i g n : − 0.25 e m ; " > < / s p a n > < s p a n c l a s s = " m o r d m a t h n o r m a l " > b < / s p a n > < s p a n c l a s s = " m c l o s e " > < s p a n c l a s s = " m c l o s e " > ) < / s p a n > < s p a n c l a s s = " m s u p s u b " > < s p a n c l a s s = " v l i s t − t " > < s p a n c l a s s = " v l i s t − r " > < s p a n c l a s s = " v l i s t " s t y l e = " h e i g h t : 0.8141 e m ; " > < s p a n s t y l e = " t o p : − 3.063 e m ; m a r g i n − r i g h t : 0.05 e m ; " > < s p a n c l a s s = " p s t r u t " s t y l e = " h e i g h t : 2.7 e m ; " > < / s p a n > < s p a n c l a s s = " s i z i n g r e s e t − s i z e 6 s i z e 3 m t i g h t " > < s p a n c l a s s = " m o r d m t i g h t " > 3 < / s p a n > < / s p a n > < / s p a n > < / s p a n > < / s p a n > < / s p a n > < / s p a n > < / s p a n > < / s p a n > < / s p a n > < / s p a n > < / s p a n > . < ! − − L A T E X P R O C E S S E D 1 756993854713 − − > < / p > < p > − B i e ^ ˊ n t h ể : D ạ n g t ổ n g q u a ˊ t h ơ n l a ˋ l ậ p p h ươ n g c ủ a m ộ t t ổ n g < s p a n c l a s s = " m a t h − i n l i n e " > < s p a n c l a s s = " k a t e x " > < s p a n c l a s s = " k a t e x − m a t h m l " > < m a t h x m l n s = " h t t p : / / w w w . w 3. o r g / 1998 / M a t h / M a t h M L " > < s e m a n t i c s > < m r o w > < m o s t r e t c h y = " f a l s e " > ( < / m o > < m i > a < / m i > < m o > + < / m o > < m i > b < / m i > < m s u p > < m o s t r e t c h y = " f a l s e " > ) < / m o > < m n > 3 < / m n > < / m s u p > < m o > = < / m o > < m s u p > < m i > a < / m i > < m n > 3 < / m n > < / m s u p > < m o > + < / m o > < m n > 3 < / m n > < m s u p > < m i > a < / m i > < m n > 2 < / m n > < / m s u p > < m i > b < / m i > < m o > + < / m o > < m n > 3 < / m n > < m i > a < / m i > < m s u p > < m i > b < / m i > < m n > 2 < / m n > < / m s u p > < m o > + < / m o > < m s u p > < m i > b < / m i > < m n > 3 < / m n > < / m s u p > < / m r o w > < a n n o t a t i o n e n c o d i n g = " a p p l i c a t i o n / x − t e x " > ( a + b ) 3 = a 3 + 3 a 2 b + 3 a b 2 + b 3 < / a n n o t a t i o n > < / s e m a n t i c s > < / m a t h > < / s p a n > < s p a n c l a s s = " k a t e x − h t m l " a r i a − h i d d e n = " t r u e " > < s p a n c l a s s = " b a s e " > < s p a n c l a s s = " s t r u t " s t y l e = " h e i g h t : 1 e m ; v e r t i c a l − a l i g n : − 0.25 e m ; " > < / s p a n > < s p a n c l a s s = " m o p e n " > ( < / s p a n > < s p a n c l a s s = " m o r d m a t h n o r m a l " > a < / s p a n > < s p a n c l a s s = " m s p a c e " s t y l e = " m a r g i n − r i g h t : 0.2222 e m ; " > < / s p a n > < s p a n c l a s s = " m b i n " > + < / s p a n > < s p a n c l a s s = " m s p a c e " s t y l e = " m a r g i n − r i g h t : 0.2222 e m ; " > < / s p a n > < / s p a n > < s p a n c l a s s = " b a s e " > < s p a n c l a s s = " s t r u t " s t y l e = " h e i g h t : 1.0641 e m ; v e r t i c a l − a l i g n : − 0.25 e m ; " > < / s p a n > < s p a n c l a s s = " m o r d m a t h n o r m a l " > b < / s p a n > < s p a n c l a s s = " m c l o s e " > < s p a n c l a s s = " m c l o s e " > ) < / s p a n > < s p a n c l a s s = " m s u p s u b " > < s p a n c l a s s = " v l i s t − t " > < s p a n c l a s s = " v l i s t − r " > < s p a n c l a s s = " v l i s t " s t y l e = " h e i g h t : 0.8141 e m ; " > < s p a n s t y l e = " t o p : − 3.063 e m ; m a r g i n − r i g h t : 0.05 e m ; " > < s p a n c l a s s = " p s t r u t " s t y l e = " h e i g h t : 2.7 e m ; " > < / s p a n > < s p a n c l a s s = " s i z i n g r e s e t − s i z e 6 s i z e 3 m t i g h t " > < s p a n c l a s s = " m o r d m t i g h t " > 3 < / s p a n > < / s p a n > < / s p a n > < / s p a n > < / s p a n > < / s p a n > < / s p a n > < / s p a n > < s p a n c l a s s = " m s p a c e " s t y l e = " m a r g i n − r i g h t : 0.2778 e m ; " > < / s p a n > < s p a n c l a s s = " m r e l " > = < / s p a n > < s p a n c l a s s = " m s p a c e " s t y l e = " m a r g i n − r i g h t : 0.2778 e m ; " > < / s p a n > < / s p a n > < s p a n c l a s s = " b a s e " > < s p a n c l a s s = " s t r u t " s t y l e = " h e i g h t : 0.8974 e m ; v e r t i c a l − a l i g n : − 0.0833 e m ; " > < / s p a n > < s p a n c l a s s = " m o r d " > < s p a n c l a s s = " m o r d m a t h n o r m a l " > a < / s p a n > < s p a n c l a s s = " m s u p s u b " > < s p a n c l a s s = " v l i s t − t " > < s p a n c l a s s = " v l i s t − r " > < s p a n c l a s s = " v l i s t " s t y l e = " h e i g h t : 0.8141 e m ; " > < s p a n s t y l e = " t o p : − 3.063 e m ; m a r g i n − r i g h t : 0.05 e m ; " > < s p a n c l a s s = " p s t r u t " s t y l e = " h e i g h t : 2.7 e m ; " > < / s p a n > < s p a n c l a s s = " s i z i n g r e s e t − s i z e 6 s i z e 3 m t i g h t " > < s p a n c l a s s = " m o r d m t i g h t " > 3 < / s p a n > < / s p a n > < / s p a n > < / s p a n > < / s p a n > < / s p a n > < / s p a n > < / s p a n > < s p a n c l a s s = " m s p a c e " s t y l e = " m a r g i n − r i g h t : 0.2222 e m ; " > < / s p a n > < s p a n c l a s s = " m b i n " > + < / s p a n > < s p a n c l a s s = " m s p a c e " s t y l e = " m a r g i n − r i g h t : 0.2222 e m ; " > < / s p a n > < / s p a n > < s p a n c l a s s = " b a s e " > < s p a n c l a s s = " s t r u t " s t y l e = " h e i g h t : 0.8974 e m ; v e r t i c a l − a l i g n : − 0.0833 e m ; " > < / s p a n > < s p a n c l a s s = " m o r d " > 3 < / s p a n > < s p a n c l a s s = " m o r d " > < s p a n c l a s s = " m o r d m a t h n o r m a l " > a < / s p a n > < s p a n c l a s s = " m s u p s u b " > < s p a n c l a s s = " v l i s t − t " > < s p a n c l a s s = " v l i s t − r " > < s p a n c l a s s = " v l i s t " s t y l e = " h e i g h t : 0.8141 e m ; " > < s p a n s t y l e = " t o p : − 3.063 e m ; m a r g i n − r i g h t : 0.05 e m ; " > < s p a n c l a s s = " p s t r u t " s t y l e = " h e i g h t : 2.7 e m ; " > < / s p a n > < s p a n c l a s s = " s i z i n g r e s e t − s i z e 6 s i z e 3 m t i g h t " > < s p a n c l a s s = " m o r d m t i g h t " > 2 < / s p a n > < / s p a n > < / s p a n > < / s p a n > < / s p a n > < / s p a n > < / s p a n > < / s p a n > < s p a n c l a s s = " m o r d m a t h n o r m a l " > b < / s p a n > < s p a n c l a s s = " m s p a c e " s t y l e = " m a r g i n − r i g h t : 0.2222 e m ; " > < / s p a n > < s p a n c l a s s = " m b i n " > + < / s p a n > < s p a n c l a s s = " m s p a c e " s t y l e = " m a r g i n − r i g h t : 0.2222 e m ; " > < / s p a n > < / s p a n > < s p a n c l a s s = " b a s e " > < s p a n c l a s s = " s t r u t " s t y l e = " h e i g h t : 0.8974 e m ; v e r t i c a l − a l i g n : − 0.0833 e m ; " > < / s p a n > < s p a n c l a s s = " m o r d " > 3 < / s p a n > < s p a n c l a s s = " m o r d m a t h n o r m a l " > a < / s p a n > < s p a n c l a s s = " m o r d " > < s p a n c l a s s = " m o r d m a t h n o r m a l " > b < / s p a n > < s p a n c l a s s = " m s u p s u b " > < s p a n c l a s s = " v l i s t − t " > < s p a n c l a s s = " v l i s t − r " > < s p a n c l a s s = " v l i s t " s t y l e = " h e i g h t : 0.8141 e m ; " > < s p a n s t y l e = " t o p : − 3.063 e m ; m a r g i n − r i g h t : 0.05 e m ; " > < s p a n c l a s s = " p s t r u t " s t y l e = " h e i g h t : 2.7 e m ; " > < / s p a n > < s p a n c l a s s = " s i z i n g r e s e t − s i z e 6 s i z e 3 m t i g h t " > < s p a n c l a s s = " m o r d m t i g h t " > 2 < / s p a n > < / s p a n > < / s p a n > < / s p a n > < / s p a n > < / s p a n > < / s p a n > < / s p a n > < s p a n c l a s s = " m s p a c e " s t y l e = " m a r g i n − r i g h t : 0.2222 e m ; " > < / s p a n > < s p a n c l a s s = " m b i n " > + < / s p a n > < s p a n c l a s s = " m s p a c e " s t y l e = " m a r g i n − r i g h t : 0.2222 e m ; " > < / s p a n > < / s p a n > < s p a n c l a s s = " b a s e " > < s p a n c l a s s = " s t r u t " s t y l e = " h e i g h t : 0.8141 e m ; " > < / s p a n > < s p a n c l a s s = " m o r d " > < s p a n c l a s s = " m o r d m a t h n o r m a l " > b < / s p a n > < s p a n c l a s s = " m s u p s u b " > < s p a n c l a s s = " v l i s t − t " > < s p a n c l a s s = " v l i s t − r " > < s p a n c l a s s = " v l i s t " s t y l e = " h e i g h t : 0.8141 e m ; " > < s p a n s t y l e = " t o p : − 3.063 e m ; m a r g i n − r i g h t : 0.05 e m ; " > < s p a n c l a s s = " p s t r u t " s t y l e = " h e i g h t : 2.7 e m ; " > < / s p a n > < s p a n c l a s s = " s i z i n g r e s e t − s i z e 6 s i z e 3 m t i g h t " > < s p a n c l a s s = " m o r d m t i g h t " > 3 < / s p a n > < / s p a n > < / s p a n > < / s p a n > < / s p a n > < / s p a n > < / s p a n > < / s p a n > < / s p a n > < / s p a n > < / s p a n > < / s p a n > . < ! − − L A T E X P R O C E S S E D 1 756993854714 − − > < / p > < h 2 > < s t r o n g > 3. V ı ˊ d ụ m i n h h ọ a c h i t i e ^ ˊ t < / s t r o n g > < / h 2 > < h 2 > < s t r o n g > 3.1 V ı ˊ d ụ c ơ b ả n < / s t r o n g > < / h 2 > < p > < s t r o n g > V ı ˊ d ụ : T ı ˊ n h < s p a n c l a s s = " m a t h − i n l i n e " > < s p a n c l a s s = " k a t e x " > < s p a n c l a s s = " k a t e x − m a t h m l " > < m a t h x m l n s = " h t t p : / / w w w . w 3. o r g / 1998 / M a t h / M a t h M L " > < s e m a n t i c s > < m r o w > < m o s t r e t c h y = " f a l s e " > ( < / m o > < m n > 2 < / m n > < m o > − < / m o > < m n > 1 < / m n > < m s u p > < m o s t r e t c h y = " f a l s e " > ) < / m o > < m n > 3 < / m n > < / m s u p > < / m r o w > < a n n o t a t i o n e n c o d i n g = " a p p l i c a t i o n / x − t e x " > ( 2 − 1 ) 3 < / a n n o t a t i o n > < / s e m a n t i c s > < / m a t h > < / s p a n > < s p a n c l a s s = " k a t e x − h t m l " a r i a − h i d d e n = " t r u e " > < s p a n c l a s s = " b a s e " > < s p a n c l a s s = " s t r u t " s t y l e = " h e i g h t : 1 e m ; v e r t i c a l − a l i g n : − 0.25 e m ; " > < / s p a n > < s p a n c l a s s = " m o p e n " > ( < / s p a n > < s p a n c l a s s = " m o r d " > 2 < / s p a n > < s p a n c l a s s = " m s p a c e " s t y l e = " m a r g i n − r i g h t : 0.2222 e m ; " > < / s p a n > < s p a n c l a s s = " m b i n " > − < / s p a n > < s p a n c l a s s = " m s p a c e " s t y l e = " m a r g i n − r i g h t : 0.2222 e m ; " > < / s p a n > < / s p a n > < s p a n c l a s s = " b a s e " > < s p a n c l a s s = " s t r u t " s t y l e = " h e i g h t : 1.0641 e m ; v e r t i c a l − a l i g n : − 0.25 e m ; " > < / s p a n > < s p a n c l a s s = " m o r d " > 1 < / s p a n > < s p a n c l a s s = " m c l o s e " > < s p a n c l a s s = " m c l o s e " > ) < / s p a n > < s p a n c l a s s = " m s u p s u b " > < s p a n c l a s s = " v l i s t − t " > < s p a n c l a s s = " v l i s t − r " > < s p a n c l a s s = " v l i s t " s t y l e = " h e i g h t : 0.8141 e m ; " > < s p a n s t y l e = " t o p : − 3.063 e m ; m a r g i n − r i g h t : 0.05 e m ; " > < s p a n c l a s s = " p s t r u t " s t y l e = " h e i g h t : 2.7 e m ; " > < / s p a n > < s p a n c l a s s = " s i z i n g r e s e t − s i z e 6 s i z e 3 m t i g h t " > < s p a n c l a s s = " m o r d m t i g h t " > 3 < / s p a n > < / s p a n > < / s p a n > < / s p a n > < / s p a n > < / s p a n > < / s p a n > < / s p a n > < / s p a n > < / s p a n > < / s p a n > < / s p a n > . < ! − − L A T E X P R O C E S S E D 1 756993854715 − − > < / s t r o n g > < / p > < p > < e m > G i ả i t ừ n g b ướ c : < / e m > < / p > < u l > < l i > A ˊ p d ụ n g c o ^ n g t h ứ c : < s p a n c l a s s = " m a t h − i n l i n e " > < s p a n c l a s s = " k a t e x " > < s p a n c l a s s = " k a t e x − m a t h m l " > < m a t h x m l n s = " h t t p : / / w w w . w 3. o r g / 1998 / M a t h / M a t h M L " > < s e m a n t i c s > < m r o w > < m o s t r e t c h y = " f a l s e " > ( < / m o > < m i > a < / m i > < m o > − < / m o > < m i > b < / m i > < m s u p > < m o s t r e t c h y = " f a l s e " > ) < / m o > < m n > 3 < / m n > < / m s u p > < m o > = < / m o > < m s u p > < m i > a < / m i > < m n > 3 < / m n > < / m s u p > < m o > − < / m o > < m n > 3 < / m n > < m s u p > < m i > a < / m i > < m n > 2 < / m n > < / m s u p > < m i > b < / m i > < m o > + < / m o > < m n > 3 < / m n > < m i > a < / m i > < m s u p > < m i > b < / m i > < m n > 2 < / m n > < / m s u p > < m o > − < / m o > < m s u p > < m i > b < / m i > < m n > 3 < / m n > < / m s u p > < / m r o w > < a n n o t a t i o n e n c o d i n g = " a p p l i c a t i o n / x − t e x " > ( a − b ) 3 = a 3 − 3 a 2 b + 3 a b 2 − b 3 < / a n n o t a t i o n > < / s e m a n t i c s > < / m a t h > < / s p a n > < s p a n c l a s s = " k a t e x − h t m l " a r i a − h i d d e n = " t r u e " > < s p a n c l a s s = " b a s e " > < s p a n c l a s s = " s t r u t " s t y l e = " h e i g h t : 1 e m ; v e r t i c a l − a l i g n : − 0.25 e m ; " > < / s p a n > < s p a n c l a s s = " m o p e n " > ( < / s p a n > < s p a n c l a s s = " m o r d m a t h n o r m a l " > a < / s p a n > < s p a n c l a s s = " m s p a c e " s t y l e = " m a r g i n − r i g h t : 0.2222 e m ; " > < / s p a n > < s p a n c l a s s = " m b i n " > − < / s p a n > < s p a n c l a s s = " m s p a c e " s t y l e = " m a r g i n − r i g h t : 0.2222 e m ; " > < / s p a n > < / s p a n > < s p a n c l a s s = " b a s e " > < s p a n c l a s s = " s t r u t " s t y l e = " h e i g h t : 1.0641 e m ; v e r t i c a l − a l i g n : − 0.25 e m ; " > < / s p a n > < s p a n c l a s s = " m o r d m a t h n o r m a l " > b < / s p a n > < s p a n c l a s s = " m c l o s e " > < s p a n c l a s s = " m c l o s e " > ) < / s p a n > < s p a n c l a s s = " m s u p s u b " > < s p a n c l a s s = " v l i s t − t " > < s p a n c l a s s = " v l i s t − r " > < s p a n c l a s s = " v l i s t " s t y l e = " h e i g h t : 0.8141 e m ; " > < s p a n s t y l e = " t o p : − 3.063 e m ; m a r g i n − r i g h t : 0.05 e m ; " > < s p a n c l a s s = " p s t r u t " s t y l e = " h e i g h t : 2.7 e m ; " > < / s p a n > < s p a n c l a s s = " s i z i n g r e s e t − s i z e 6 s i z e 3 m t i g h t " > < s p a n c l a s s = " m o r d m t i g h t " > 3 < / s p a n > < / s p a n > < / s p a n > < / s p a n > < / s p a n > < / s p a n > < / s p a n > < / s p a n > < s p a n c l a s s = " m s p a c e " s t y l e = " m a r g i n − r i g h t : 0.2778 e m ; " > < / s p a n > < s p a n c l a s s = " m r e l " > = < / s p a n > < s p a n c l a s s = " m s p a c e " s t y l e = " m a r g i n − r i g h t : 0.2778 e m ; " > < / s p a n > < / s p a n > < s p a n c l a s s = " b a s e " > < s p a n c l a s s = " s t r u t " s t y l e = " h e i g h t : 0.8974 e m ; v e r t i c a l − a l i g n : − 0.0833 e m ; " > < / s p a n > < s p a n c l a s s = " m o r d " > < s p a n c l a s s = " m o r d m a t h n o r m a l " > a < / s p a n > < s p a n c l a s s = " m s u p s u b " > < s p a n c l a s s = " v l i s t − t " > < s p a n c l a s s = " v l i s t − r " > < s p a n c l a s s = " v l i s t " s t y l e = " h e i g h t : 0.8141 e m ; " > < s p a n s t y l e = " t o p : − 3.063 e m ; m a r g i n − r i g h t : 0.05 e m ; " > < s p a n c l a s s = " p s t r u t " s t y l e = " h e i g h t : 2.7 e m ; " > < / s p a n > < s p a n c l a s s = " s i z i n g r e s e t − s i z e 6 s i z e 3 m t i g h t " > < s p a n c l a s s = " m o r d m t i g h t " > 3 < / s p a n > < / s p a n > < / s p a n > < / s p a n > < / s p a n > < / s p a n > < / s p a n > < / s p a n > < s p a n c l a s s = " m s p a c e " s t y l e = " m a r g i n − r i g h t : 0.2222 e m ; " > < / s p a n > < s p a n c l a s s = " m b i n " > − < / s p a n > < s p a n c l a s s = " m s p a c e " s t y l e = " m a r g i n − r i g h t : 0.2222 e m ; " > < / s p a n > < / s p a n > < s p a n c l a s s = " b a s e " > < s p a n c l a s s = " s t r u t " s t y l e = " h e i g h t : 0.8974 e m ; v e r t i c a l − a l i g n : − 0.0833 e m ; " > < / s p a n > < s p a n c l a s s = " m o r d " > 3 < / s p a n > < s p a n c l a s s = " m o r d " > < s p a n c l a s s = " m o r d m a t h n o r m a l " > a < / s p a n > < s p a n c l a s s = " m s u p s u b " > < s p a n c l a s s = " v l i s t − t " > < s p a n c l a s s = " v l i s t − r " > < s p a n c l a s s = " v l i s t " s t y l e = " h e i g h t : 0.8141 e m ; " > < s p a n s t y l e = " t o p : − 3.063 e m ; m a r g i n − r i g h t : 0.05 e m ; " > < s p a n c l a s s = " p s t r u t " s t y l e = " h e i g h t : 2.7 e m ; " > < / s p a n > < s p a n c l a s s = " s i z i n g r e s e t − s i z e 6 s i z e 3 m t i g h t " > < s p a n c l a s s = " m o r d m t i g h t " > 2 < / s p a n > < / s p a n > < / s p a n > < / s p a n > < / s p a n > < / s p a n > < / s p a n > < / s p a n > < s p a n c l a s s = " m o r d m a t h n o r m a l " > b < / s p a n > < s p a n c l a s s = " m s p a c e " s t y l e = " m a r g i n − r i g h t : 0.2222 e m ; " > < / s p a n > < s p a n c l a s s = " m b i n " > + < / s p a n > < s p a n c l a s s = " m s p a c e " s t y l e = " m a r g i n − r i g h t : 0.2222 e m ; " > < / s p a n > < / s p a n > < s p a n c l a s s = " b a s e " > < s p a n c l a s s = " s t r u t " s t y l e = " h e i g h t : 0.8974 e m ; v e r t i c a l − a l i g n : − 0.0833 e m ; " > < / s p a n > < s p a n c l a s s = " m o r d " > 3 < / s p a n > < s p a n c l a s s = " m o r d m a t h n o r m a l " > a < / s p a n > < s p a n c l a s s = " m o r d " > < s p a n c l a s s = " m o r d m a t h n o r m a l " > b < / s p a n > < s p a n c l a s s = " m s u p s u b " > < s p a n c l a s s = " v l i s t − t " > < s p a n c l a s s = " v l i s t − r " > < s p a n c l a s s = " v l i s t " s t y l e = " h e i g h t : 0.8141 e m ; " > < s p a n s t y l e = " t o p : − 3.063 e m ; m a r g i n − r i g h t : 0.05 e m ; " > < s p a n c l a s s = " p s t r u t " s t y l e = " h e i g h t : 2.7 e m ; " > < / s p a n > < s p a n c l a s s = " s i z i n g r e s e t − s i z e 6 s i z e 3 m t i g h t " > < s p a n c l a s s = " m o r d m t i g h t " > 2 < / s p a n > < / s p a n > < / s p a n > < / s p a n > < / s p a n > < / s p a n > < / s p a n > < / s p a n > < s p a n c l a s s = " m s p a c e " s t y l e = " m a r g i n − r i g h t : 0.2222 e m ; " > < / s p a n > < s p a n c l a s s = " m b i n " > − < / s p a n > < s p a n c l a s s = " m s p a c e " s t y l e = " m a r g i n − r i g h t : 0.2222 e m ; " > < / s p a n > < / s p a n > < s p a n c l a s s = " b a s e " > < s p a n c l a s s = " s t r u t " s t y l e = " h e i g h t : 0.8141 e m ; " > < / s p a n > < s p a n c l a s s = " m o r d " > < s p a n c l a s s = " m o r d m a t h n o r m a l " > b < / s p a n > < s p a n c l a s s = " m s u p s u b " > < s p a n c l a s s = " v l i s t − t " > < s p a n c l a s s = " v l i s t − r " > < s p a n c l a s s = " v l i s t " s t y l e = " h e i g h t : 0.8141 e m ; " > < s p a n s t y l e = " t o p : − 3.063 e m ; m a r g i n − r i g h t : 0.05 e m ; " > < s p a n c l a s s = " p s t r u t " s t y l e = " h e i g h t : 2.7 e m ; " > < / s p a n > < s p a n c l a s s = " s i z i n g r e s e t − s i z e 6 s i z e 3 m t i g h t " > < s p a n c l a s s = " m o r d m t i g h t " > 3 < / s p a n > < / s p a n > < / s p a n > < / s p a n > < / s p a n > < / s p a n > < / s p a n > < / s p a n > < / s p a n > < / s p a n > < / s p a n > < / s p a n > v ớ i < s p a n c l a s s = " m a t h − i n l i n e " > < s p a n c l a s s = " k a t e x " > < s p a n c l a s s = " k a t e x − m a t h m l " > < m a t h x m l n s = " h t t p : / / w w w . w 3. o r g / 1998 / M a t h / M a t h M L " > < s e m a n t i c s > < m r o w > < m i > a < / m i > < m o > = < / m o > < m n > 2 < / m n > < / m r o w > < a n n o t a t i o n e n c o d i n g = " a p p l i c a t i o n / x − t e x " > a = 2 < / a n n o t a t i o n > < / s e m a n t i c s > < / m a t h > < / s p a n > < s p a n c l a s s = " k a t e x − h t m l " a r i a − h i d d e n = " t r u e " > < s p a n c l a s s = " b a s e " > < s p a n c l a s s = " s t r u t " s t y l e = " h e i g h t : 0.4306 e m ; " > < / s p a n > < s p a n c l a s s = " m o r d m a t h n o r m a l " > a < / s p a n > < s p a n c l a s s = " m s p a c e " s t y l e = " m a r g i n − r i g h t : 0.2778 e m ; " > < / s p a n > < s p a n c l a s s = " m r e l " > = < / s p a n > < s p a n c l a s s = " m s p a c e " s t y l e = " m a r g i n − r i g h t : 0.2778 e m ; " > < / s p a n > < / s p a n > < s p a n c l a s s = " b a s e " > < s p a n c l a s s = " s t r u t " s t y l e = " h e i g h t : 0.6444 e m ; " > < / s p a n > < s p a n c l a s s = " m o r d " > 2 < / s p a n > < / s p a n > < / s p a n > < / s p a n > < / s p a n > , < s p a n c l a s s = " m a t h − i n l i n e " > < s p a n c l a s s = " k a t e x " > < s p a n c l a s s = " k a t e x − m a t h m l " > < m a t h x m l n s = " h t t p : / / w w w . w 3. o r g / 1998 / M a t h / M a t h M L " > < s e m a n t i c s > < m r o w > < m i > b < / m i > < m o > = < / m o > < m n > 1 < / m n > < / m r o w > < a n n o t a t i o n e n c o d i n g = " a p p l i c a t i o n / x − t e x " > b = 1 < / a n n o t a t i o n > < / s e m a n t i c s > < / m a t h > < / s p a n > < s p a n c l a s s = " k a t e x − h t m l " a r i a − h i d d e n = " t r u e " > < s p a n c l a s s = " b a s e " > < s p a n c l a s s = " s t r u t " s t y l e = " h e i g h t : 0.6944 e m ; " > < / s p a n > < s p a n c l a s s = " m o r d m a t h n o r m a l " > b < / s p a n > < s p a n c l a s s = " m s p a c e " s t y l e = " m a r g i n − r i g h t : 0.2778 e m ; " > < / s p a n > < s p a n c l a s s = " m r e l " > = < / s p a n > < s p a n c l a s s = " m s p a c e " s t y l e = " m a r g i n − r i g h t : 0.2778 e m ; " > < / s p a n > < / s p a n > < s p a n c l a s s = " b a s e " > < s p a n c l a s s = " s t r u t " s t y l e = " h e i g h t : 0.6444 e m ; " > < / s p a n > < s p a n c l a s s = " m o r d " > 1 < / s p a n > < / s p a n > < / s p a n > < / s p a n > < / s p a n > < ! − − L A T E X P R O C E S S E D 1 756993854716 − − > < / l i > < l i > < s p a n c l a s s = " m a t h − i n l i n e " > < s p a n c l a s s = " k a t e x " > < s p a n c l a s s = " k a t e x − m a t h m l " > < m a t h x m l n s = " h t t p : / / w w w . w 3. o r g / 1998 / M a t h / M a t h M L " > < s e m a n t i c s > < m r o w > < m s u p > < m n > 2 < / m n > < m n > 3 < / m n > < / m s u p > < m o > − < / m o > < m n > 3 < / m n > < m i > i < / m i > < m i > m < / m i > < m i > e < / m i > < m i > s < / m i > < m s u p > < m n > 2 < / m n > < m n > 2 < / m n > < / m s u p > < m i > i < / m i > < m i > m < / m i > < m i > e < / m i > < m i > s < / m i > < m n > 1 < / m n > < m o > + < / m o > < m n > 3 < / m n > < m i > i < / m i > < m i > m < / m i > < m i > e < / m i > < m i > s < / m i > < m n > 2 < / m n > < m i > i < / m i > < m i > m < / m i > < m i > e < / m i > < m i > s < / m i > < m s u p > < m n > 1 < / m n > < m n > 2 < / m n > < / m s u p > < m o > − < / m o > < m s u p > < m n > 1 < / m n > < m n > 3 < / m n > < / m s u p > < m o > = < / m o > < m n > 8 < / m n > < m o > − < / m o > < m n > 12 < / m n > < m o > + < / m o > < m n > 6 < / m n > < m o > − < / m o > < m n > 1 < / m n > < m o > = < / m o > < m n > 1 < / m n > < / m r o w > < a n n o t a t i o n e n c o d i n g = " a p p l i c a t i o n / x − t e x " > 2 3 − 3 i m e s 2 2 i m e s 1 + 3 i m e s 2 i m e s 1 2 − 1 3 = 8 − 12 + 6 − 1 = 1 < / a n n o t a t i o n > < / s e m a n t i c s > < / m a t h > < / s p a n > < s p a n c l a s s = " k a t e x − h t m l " a r i a − h i d d e n = " t r u e " > < s p a n c l a s s = " b a s e " > < s p a n c l a s s = " s t r u t " s t y l e = " h e i g h t : 0.8974 e m ; v e r t i c a l − a l i g n : − 0.0833 e m ; " > < / s p a n > < s p a n c l a s s = " m o r d " > < s p a n c l a s s = " m o r d " > 2 < / s p a n > < s p a n c l a s s = " m s u p s u b " > < s p a n c l a s s = " v l i s t − t " > < s p a n c l a s s = " v l i s t − r " > < s p a n c l a s s = " v l i s t " s t y l e = " h e i g h t : 0.8141 e m ; " > < s p a n s t y l e = " t o p : − 3.063 e m ; m a r g i n − r i g h t : 0.05 e m ; " > < s p a n c l a s s = " p s t r u t " s t y l e = " h e i g h t : 2.7 e m ; " > < / s p a n > < s p a n c l a s s = " s i z i n g r e s e t − s i z e 6 s i z e 3 m t i g h t " > < s p a n c l a s s = " m o r d m t i g h t " > 3 < / s p a n > < / s p a n > < / s p a n > < / s p a n > < / s p a n > < / s p a n > < / s p a n > < / s p a n > < s p a n c l a s s = " m s p a c e " s t y l e = " m a r g i n − r i g h t : 0.2222 e m ; " > < / s p a n > < s p a n c l a s s = " m b i n " > − < / s p a n > < s p a n c l a s s = " m s p a c e " s t y l e = " m a r g i n − r i g h t : 0.2222 e m ; " > < / s p a n > < / s p a n > < s p a n c l a s s = " b a s e " > < s p a n c l a s s = " s t r u t " s t y l e = " h e i g h t : 0.8974 e m ; v e r t i c a l − a l i g n : − 0.0833 e m ; " > < / s p a n > < s p a n c l a s s = " m o r d " > 3 < / s p a n > < s p a n c l a s s = " m o r d m a t h n o r m a l " > i m < / s p a n > < s p a n c l a s s = " m o r d m a t h n o r m a l " > e s < / s p a n > < s p a n c l a s s = " m o r d " > < s p a n c l a s s = " m o r d " > 2 < / s p a n > < s p a n c l a s s = " m s u p s u b " > < s p a n c l a s s = " v l i s t − t " > < s p a n c l a s s = " v l i s t − r " > < s p a n c l a s s = " v l i s t " s t y l e = " h e i g h t : 0.8141 e m ; " > < s p a n s t y l e = " t o p : − 3.063 e m ; m a r g i n − r i g h t : 0.05 e m ; " > < s p a n c l a s s = " p s t r u t " s t y l e = " h e i g h t : 2.7 e m ; " > < / s p a n > < s p a n c l a s s = " s i z i n g r e s e t − s i z e 6 s i z e 3 m t i g h t " > < s p a n c l a s s = " m o r d m t i g h t " > 2 < / s p a n > < / s p a n > < / s p a n > < / s p a n > < / s p a n > < / s p a n > < / s p a n > < / s p a n > < s p a n c l a s s = " m o r d m a t h n o r m a l " > i m < / s p a n > < s p a n c l a s s = " m o r d m a t h n o r m a l " > e s < / s p a n > < s p a n c l a s s = " m o r d " > 1 < / s p a n > < s p a n c l a s s = " m s p a c e " s t y l e = " m a r g i n − r i g h t : 0.2222 e m ; " > < / s p a n > < s p a n c l a s s = " m b i n " > + < / s p a n > < s p a n c l a s s = " m s p a c e " s t y l e = " m a r g i n − r i g h t : 0.2222 e m ; " > < / s p a n > < / s p a n > < s p a n c l a s s = " b a s e " > < s p a n c l a s s = " s t r u t " s t y l e = " h e i g h t : 0.8974 e m ; v e r t i c a l − a l i g n : − 0.0833 e m ; " > < / s p a n > < s p a n c l a s s = " m o r d " > 3 < / s p a n > < s p a n c l a s s = " m o r d m a t h n o r m a l " > i m < / s p a n > < s p a n c l a s s = " m o r d m a t h n o r m a l " > e s < / s p a n > < s p a n c l a s s = " m o r d " > 2 < / s p a n > < s p a n c l a s s = " m o r d m a t h n o r m a l " > i m < / s p a n > < s p a n c l a s s = " m o r d m a t h n o r m a l " > e s < / s p a n > < s p a n c l a s s = " m o r d " > < s p a n c l a s s = " m o r d " > 1 < / s p a n > < s p a n c l a s s = " m s u p s u b " > < s p a n c l a s s = " v l i s t − t " > < s p a n c l a s s = " v l i s t − r " > < s p a n c l a s s = " v l i s t " s t y l e = " h e i g h t : 0.8141 e m ; " > < s p a n s t y l e = " t o p : − 3.063 e m ; m a r g i n − r i g h t : 0.05 e m ; " > < s p a n c l a s s = " p s t r u t " s t y l e = " h e i g h t : 2.7 e m ; " > < / s p a n > < s p a n c l a s s = " s i z i n g r e s e t − s i z e 6 s i z e 3 m t i g h t " > < s p a n c l a s s = " m o r d m t i g h t " > 2 < / s p a n > < / s p a n > < / s p a n > < / s p a n > < / s p a n > < / s p a n > < / s p a n > < / s p a n > < s p a n c l a s s = " m s p a c e " s t y l e = " m a r g i n − r i g h t : 0.2222 e m ; " > < / s p a n > < s p a n c l a s s = " m b i n " > − < / s p a n > < s p a n c l a s s = " m s p a c e " s t y l e = " m a r g i n − r i g h t : 0.2222 e m ; " > < / s p a n > < / s p a n > < s p a n c l a s s = " b a s e " > < s p a n c l a s s = " s t r u t " s t y l e = " h e i g h t : 0.8141 e m ; " > < / s p a n > < s p a n c l a s s = " m o r d " > < s p a n c l a s s = " m o r d " > 1 < / s p a n > < s p a n c l a s s = " m s u p s u b " > < s p a n c l a s s = " v l i s t − t " > < s p a n c l a s s = " v l i s t − r " > < s p a n c l a s s = " v l i s t " s t y l e = " h e i g h t : 0.8141 e m ; " > < s p a n s t y l e = " t o p : − 3.063 e m ; m a r g i n − r i g h t : 0.05 e m ; " > < s p a n c l a s s = " p s t r u t " s t y l e = " h e i g h t : 2.7 e m ; " > < / s p a n > < s p a n c l a s s = " s i z i n g r e s e t − s i z e 6 s i z e 3 m t i g h t " > < s p a n c l a s s = " m o r d m t i g h t " > 3 < / s p a n > < / s p a n > < / s p a n > < / s p a n > < / s p a n > < / s p a n > < / s p a n > < / s p a n > < s p a n c l a s s = " m s p a c e " s t y l e = " m a r g i n − r i g h t : 0.2778 e m ; " > < / s p a n > < s p a n c l a s s = " m r e l " > = < / s p a n > < s p a n c l a s s = " m s p a c e " s t y l e = " m a r g i n − r i g h t : 0.2778 e m ; " > < / s p a n > < / s p a n > < s p a n c l a s s = " b a s e " > < s p a n c l a s s = " s t r u t " s t y l e = " h e i g h t : 0.7278 e m ; v e r t i c a l − a l i g n : − 0.0833 e m ; " > < / s p a n > < s p a n c l a s s = " m o r d " > 8 < / s p a n > < s p a n c l a s s = " m s p a c e " s t y l e = " m a r g i n − r i g h t : 0.2222 e m ; " > < / s p a n > < s p a n c l a s s = " m b i n " > − < / s p a n > < s p a n c l a s s = " m s p a c e " s t y l e = " m a r g i n − r i g h t : 0.2222 e m ; " > < / s p a n > < / s p a n > < s p a n c l a s s = " b a s e " > < s p a n c l a s s = " s t r u t " s t y l e = " h e i g h t : 0.7278 e m ; v e r t i c a l − a l i g n : − 0.0833 e m ; " > < / s p a n > < s p a n c l a s s = " m o r d " > 12 < / s p a n > < s p a n c l a s s = " m s p a c e " s t y l e = " m a r g i n − r i g h t : 0.2222 e m ; " > < / s p a n > < s p a n c l a s s = " m b i n " > + < / s p a n > < s p a n c l a s s = " m s p a c e " s t y l e = " m a r g i n − r i g h t : 0.2222 e m ; " > < / s p a n > < / s p a n > < s p a n c l a s s = " b a s e " > < s p a n c l a s s = " s t r u t " s t y l e = " h e i g h t : 0.7278 e m ; v e r t i c a l − a l i g n : − 0.0833 e m ; " > < / s p a n > < s p a n c l a s s = " m o r d " > 6 < / s p a n > < s p a n c l a s s = " m s p a c e " s t y l e = " m a r g i n − r i g h t : 0.2222 e m ; " > < / s p a n > < s p a n c l a s s = " m b i n " > − < / s p a n > < s p a n c l a s s = " m s p a c e " s t y l e = " m a r g i n − r i g h t : 0.2222 e m ; " > < / s p a n > < / s p a n > < s p a n c l a s s = " b a s e " > < s p a n c l a s s = " s t r u t " s t y l e = " h e i g h t : 0.6444 e m ; " > < / s p a n > < s p a n c l a s s = " m o r d " > 1 < / s p a n > < s p a n c l a s s = " m s p a c e " s t y l e = " m a r g i n − r i g h t : 0.2778 e m ; " > < / s p a n > < s p a n c l a s s = " m r e l " > = < / s p a n > < s p a n c l a s s = " m s p a c e " s t y l e = " m a r g i n − r i g h t : 0.2778 e m ; " > < / s p a n > < / s p a n > < s p a n c l a s s = " b a s e " > < s p a n c l a s s = " s t r u t " s t y l e = " h e i g h t : 0.6444 e m ; " > < / s p a n > < s p a n c l a s s = " m o r d " > 1 < / s p a n > < / s p a n > < / s p a n > < / s p a n > < / s p a n > < ! − − L A T E X P R O C E S S E D 1 756993854718 − − > < / l i > < / u l > < p > < s t r o n g > L ư u y ˊ : C ẩ n t h ậ n k h i t h a y s o ^ ˊ , đừ n g q u e ^ n d a ^ ˊ u t r ừ ! < / s t r o n g > < / p > < h 2 > < s t r o n g > 3.2 V ı ˊ d ụ n a ^ n g c a o < / s t r o n g > < / h 2 > < p > < s t r o n g > V ı ˊ d ụ : R u ˊ t g ọ n b i ể u t h ứ c < s p a n c l a s s = " m a t h − i n l i n e " > < s p a n c l a s s = " k a t e x " > < s p a n c l a s s = " k a t e x − m a t h m l " > < m a t h x m l n s = " h t t p : / / w w w . w 3. o r g / 1998 / M a t h / M a t h M L " > < s e m a n t i c s > < m r o w > < m o s t r e t c h y = " f a l s e " > ( < / m o > < m i > x < / m i > < m o > − < / m o > < m n > 2 < / m n > < m i > y < / m i > < m s u p > < m o s t r e t c h y = " f a l s e " > ) < / m o > < m n > 3 < / m n > < / m s u p > < / m r o w > < a n n o t a t i o n e n c o d i n g = " a p p l i c a t i o n / x − t e x " > ( x − 2 y ) 3 < / a n n o t a t i o n > < / s e m a n t i c s > < / m a t h > < / s p a n > < s p a n c l a s s = " k a t e x − h t m l " a r i a − h i d d e n = " t r u e " > < s p a n c l a s s = " b a s e " > < s p a n c l a s s = " s t r u t " s t y l e = " h e i g h t : 1 e m ; v e r t i c a l − a l i g n : − 0.25 e m ; " > < / s p a n > < s p a n c l a s s = " m o p e n " > ( < / s p a n > < s p a n c l a s s = " m o r d m a t h n o r m a l " > x < / s p a n > < s p a n c l a s s = " m s p a c e " s t y l e = " m a r g i n − r i g h t : 0.2222 e m ; " > < / s p a n > < s p a n c l a s s = " m b i n " > − < / s p a n > < s p a n c l a s s = " m s p a c e " s t y l e = " m a r g i n − r i g h t : 0.2222 e m ; " > < / s p a n > < / s p a n > < s p a n c l a s s = " b a s e " > < s p a n c l a s s = " s t r u t " s t y l e = " h e i g h t : 1.0641 e m ; v e r t i c a l − a l i g n : − 0.25 e m ; " > < / s p a n > < s p a n c l a s s = " m o r d " > 2 < / s p a n > < s p a n c l a s s = " m o r d m a t h n o r m a l " s t y l e = " m a r g i n − r i g h t : 0.03588 e m ; " > y < / s p a n > < s p a n c l a s s = " m c l o s e " > < s p a n c l a s s = " m c l o s e " > ) < / s p a n > < s p a n c l a s s = " m s u p s u b " > < s p a n c l a s s = " v l i s t − t " > < s p a n c l a s s = " v l i s t − r " > < s p a n c l a s s = " v l i s t " s t y l e = " h e i g h t : 0.8141 e m ; " > < s p a n s t y l e = " t o p : − 3.063 e m ; m a r g i n − r i g h t : 0.05 e m ; " > < s p a n c l a s s = " p s t r u t " s t y l e = " h e i g h t : 2.7 e m ; " > < / s p a n > < s p a n c l a s s = " s i z i n g r e s e t − s i z e 6 s i z e 3 m t i g h t " > < s p a n c l a s s = " m o r d m t i g h t " > 3 < / s p a n > < / s p a n > < / s p a n > < / s p a n > < / s p a n > < / s p a n > < / s p a n > < / s p a n > < / s p a n > < / s p a n > < / s p a n > < / s p a n > . < ! − − L A T E X P R O C E S S E D 1 756993854718 − − > < / s t r o n g > < / p > < p > < e m > A ˊ p d ụ n g c o ^ n g t h ứ c : < / e m > < / p > < d i v c l a s s = " m a t h − b l o c k m y − 4 t e x t − c e n t e r " > < d i v c l a s s = " m a t h − d i s p l a y " r o l e = " i m g " a r i a − l a b e l = " M a t h e m a t i c a l e x p r e s s i o n : </div><p>- <strong>Cách ghi nhớ hiệu quả:</strong>Hãy nhớ đúng thứ tự dấu “+, -, +, -” và lưu ý hệ số 1-3-3-1 kèm theo lũy thừa giảm dần của<span class="math-inline"><span class="katex"><span class="katex-mathml"><math xmlns="http://www.w3.org/1998/Math/MathML"><semantics><mrow><mi>a</mi></mrow><annotation encoding="application/x-tex">a</annotation></semantics></math></span><span class="katex-html" aria-hidden="true"><span class="base"><span class="strut" style="height:0.4306em;"></span><span class="mord mathnormal">a</span></span></span></span></span>và tăng dần của<span class="math-inline"><span class="katex"><span class="katex-mathml"><math xmlns="http://www.w3.org/1998/Math/MathML"><semantics><mrow><mi>b</mi></mrow><annotation encoding="application/x-tex">b</annotation></semantics></math></span><span class="katex-html" aria-hidden="true"><span class="base"><span class="strut" style="height:0.6944em;"></span><span class="mord mathnormal">b</span></span></span></span></span>trong từng hạng tử.<!--LATEX_PROCESSED_1756993854712--></p><p>- Điều kiện sử dụng: Chỉ sử dụng khi hiệu ở cùng dạng<span class="math-inline"><span class="katex"><span class="katex-mathml"><math xmlns="http://www.w3.org/1998/Math/MathML"><semantics><mrow><mo stretchy="false">(</mo><mi>a</mi><mo>−</mo><mi>b</mi><msup><mo stretchy="false">)</mo><mn>3</mn></msup></mrow><annotation encoding="application/x-tex">(a-b)^3</annotation></semantics></math></span><span class="katex-html" aria-hidden="true"><span class="base"><span class="strut" style="height:1em;vertical-align:-0.25em;"></span><span class="mopen">(</span><span class="mord mathnormal">a</span><span class="mspace" style="margin-right:0.2222em;"></span><span class="mbin">−</span><span class="mspace" style="margin-right:0.2222em;"></span></span><span class="base"><span class="strut" style="height:1.0641em;vertical-align:-0.25em;"></span><span class="mord mathnormal">b</span><span class="mclose"><span class="mclose">)</span><span class="msupsub"><span class="vlist-t"><span class="vlist-r"><span class="vlist" style="height:0.8141em;"><span style="top:-3.063em;margin-right:0.05em;"><span class="pstrut" style="height:2.7em;"></span><span class="sizing reset-size6 size3 mtight"><span class="mord mtight">3</span></span></span></span></span></span></span></span></span></span></span></span>.<!--LATEX_PROCESSED_1756993854713--></p><p>- Biến thể: Dạng tổng quát hơn là lập phương của một tổng<span class="math-inline"><span class="katex"><span class="katex-mathml"><math xmlns="http://www.w3.org/1998/Math/MathML"><semantics><mrow><mo stretchy="false">(</mo><mi>a</mi><mo>+</mo><mi>b</mi><msup><mo stretchy="false">)</mo><mn>3</mn></msup><mo>=</mo><msup><mi>a</mi><mn>3</mn></msup><mo>+</mo><mn>3</mn><msup><mi>a</mi><mn>2</mn></msup><mi>b</mi><mo>+</mo><mn>3</mn><mi>a</mi><msup><mi>b</mi><mn>2</mn></msup><mo>+</mo><msup><mi>b</mi><mn>3</mn></msup></mrow><annotation encoding="application/x-tex">(a+b)^3 = a^3 + 3a^2b + 3ab^2 + b^3</annotation></semantics></math></span><span class="katex-html" aria-hidden="true"><span class="base"><span class="strut" style="height:1em;vertical-align:-0.25em;"></span><span class="mopen">(</span><span class="mord mathnormal">a</span><span class="mspace" style="margin-right:0.2222em;"></span><span class="mbin">+</span><span class="mspace" style="margin-right:0.2222em;"></span></span><span class="base"><span class="strut" style="height:1.0641em;vertical-align:-0.25em;"></span><span class="mord mathnormal">b</span><span class="mclose"><span class="mclose">)</span><span class="msupsub"><span class="vlist-t"><span class="vlist-r"><span class="vlist" style="height:0.8141em;"><span style="top:-3.063em;margin-right:0.05em;"><span class="pstrut" style="height:2.7em;"></span><span class="sizing reset-size6 size3 mtight"><span class="mord mtight">3</span></span></span></span></span></span></span></span><span class="mspace" style="margin-right:0.2778em;"></span><span class="mrel">=</span><span class="mspace" style="margin-right:0.2778em;"></span></span><span class="base"><span class="strut" style="height:0.8974em;vertical-align:-0.0833em;"></span><span class="mord"><span class="mord mathnormal">a</span><span class="msupsub"><span class="vlist-t"><span class="vlist-r"><span class="vlist" style="height:0.8141em;"><span style="top:-3.063em;margin-right:0.05em;"><span class="pstrut" style="height:2.7em;"></span><span class="sizing reset-size6 size3 mtight"><span class="mord mtight">3</span></span></span></span></span></span></span></span><span class="mspace" style="margin-right:0.2222em;"></span><span class="mbin">+</span><span class="mspace" style="margin-right:0.2222em;"></span></span><span class="base"><span class="strut" style="height:0.8974em;vertical-align:-0.0833em;"></span><span class="mord">3</span><span class="mord"><span class="mord mathnormal">a</span><span class="msupsub"><span class="vlist-t"><span class="vlist-r"><span class="vlist" style="height:0.8141em;"><span style="top:-3.063em;margin-right:0.05em;"><span class="pstrut" style="height:2.7em;"></span><span class="sizing reset-size6 size3 mtight"><span class="mord mtight">2</span></span></span></span></span></span></span></span><span class="mord mathnormal">b</span><span class="mspace" style="margin-right:0.2222em;"></span><span class="mbin">+</span><span class="mspace" style="margin-right:0.2222em;"></span></span><span class="base"><span class="strut" style="height:0.8974em;vertical-align:-0.0833em;"></span><span class="mord">3</span><span class="mord mathnormal">a</span><span class="mord"><span class="mord mathnormal">b</span><span class="msupsub"><span class="vlist-t"><span class="vlist-r"><span class="vlist" style="height:0.8141em;"><span style="top:-3.063em;margin-right:0.05em;"><span class="pstrut" style="height:2.7em;"></span><span class="sizing reset-size6 size3 mtight"><span class="mord mtight">2</span></span></span></span></span></span></span></span><span class="mspace" style="margin-right:0.2222em;"></span><span class="mbin">+</span><span class="mspace" style="margin-right:0.2222em;"></span></span><span class="base"><span class="strut" style="height:0.8141em;"></span><span class="mord"><span class="mord mathnormal">b</span><span class="msupsub"><span class="vlist-t"><span class="vlist-r"><span class="vlist" style="height:0.8141em;"><span style="top:-3.063em;margin-right:0.05em;"><span class="pstrut" style="height:2.7em;"></span><span class="sizing reset-size6 size3 mtight"><span class="mord mtight">3</span></span></span></span></span></span></span></span></span></span></span></span>.<!--LATEX_PROCESSED_1756993854714--></p><h2><strong>3. Ví dụ minh họa chi tiết</strong></h2><h2><strong>3.1 Ví dụ cơ bản</strong></h2><p><strong>Ví dụ: Tính<span class="math-inline"><span class="katex"><span class="katex-mathml"><math xmlns="http://www.w3.org/1998/Math/MathML"><semantics><mrow><mo stretchy="false">(</mo><mn>2</mn><mo>−</mo><mn>1</mn><msup><mo stretchy="false">)</mo><mn>3</mn></msup></mrow><annotation encoding="application/x-tex">(2-1)^3</annotation></semantics></math></span><span class="katex-html" aria-hidden="true"><span class="base"><span class="strut" style="height:1em;vertical-align:-0.25em;"></span><span class="mopen">(</span><span class="mord">2</span><span class="mspace" style="margin-right:0.2222em;"></span><span class="mbin">−</span><span class="mspace" style="margin-right:0.2222em;"></span></span><span class="base"><span class="strut" style="height:1.0641em;vertical-align:-0.25em;"></span><span class="mord">1</span><span class="mclose"><span class="mclose">)</span><span class="msupsub"><span class="vlist-t"><span class="vlist-r"><span class="vlist" style="height:0.8141em;"><span style="top:-3.063em;margin-right:0.05em;"><span class="pstrut" style="height:2.7em;"></span><span class="sizing reset-size6 size3 mtight"><span class="mord mtight">3</span></span></span></span></span></span></span></span></span></span></span></span>.<!--LATEX_PROCESSED_1756993854715--></strong></p><p><em>Giải từng bước:</em></p><ul><li>Áp dụng công thức:<span class="math-inline"><span class="katex"><span class="katex-mathml"><math xmlns="http://www.w3.org/1998/Math/MathML"><semantics><mrow><mo stretchy="false">(</mo><mi>a</mi><mo>−</mo><mi>b</mi><msup><mo stretchy="false">)</mo><mn>3</mn></msup><mo>=</mo><msup><mi>a</mi><mn>3</mn></msup><mo>−</mo><mn>3</mn><msup><mi>a</mi><mn>2</mn></msup><mi>b</mi><mo>+</mo><mn>3</mn><mi>a</mi><msup><mi>b</mi><mn>2</mn></msup><mo>−</mo><msup><mi>b</mi><mn>3</mn></msup></mrow><annotation encoding="application/x-tex">(a-b)^3 = a^3 - 3a^2b + 3ab^2 - b^3</annotation></semantics></math></span><span class="katex-html" aria-hidden="true"><span class="base"><span class="strut" style="height:1em;vertical-align:-0.25em;"></span><span class="mopen">(</span><span class="mord mathnormal">a</span><span class="mspace" style="margin-right:0.2222em;"></span><span class="mbin">−</span><span class="mspace" style="margin-right:0.2222em;"></span></span><span class="base"><span class="strut" style="height:1.0641em;vertical-align:-0.25em;"></span><span class="mord mathnormal">b</span><span class="mclose"><span class="mclose">)</span><span class="msupsub"><span class="vlist-t"><span class="vlist-r"><span class="vlist" style="height:0.8141em;"><span style="top:-3.063em;margin-right:0.05em;"><span class="pstrut" style="height:2.7em;"></span><span class="sizing reset-size6 size3 mtight"><span class="mord mtight">3</span></span></span></span></span></span></span></span><span class="mspace" style="margin-right:0.2778em;"></span><span class="mrel">=</span><span class="mspace" style="margin-right:0.2778em;"></span></span><span class="base"><span class="strut" style="height:0.8974em;vertical-align:-0.0833em;"></span><span class="mord"><span class="mord mathnormal">a</span><span class="msupsub"><span class="vlist-t"><span class="vlist-r"><span class="vlist" style="height:0.8141em;"><span style="top:-3.063em;margin-right:0.05em;"><span class="pstrut" style="height:2.7em;"></span><span class="sizing reset-size6 size3 mtight"><span class="mord mtight">3</span></span></span></span></span></span></span></span><span class="mspace" style="margin-right:0.2222em;"></span><span class="mbin">−</span><span class="mspace" style="margin-right:0.2222em;"></span></span><span class="base"><span class="strut" style="height:0.8974em;vertical-align:-0.0833em;"></span><span class="mord">3</span><span class="mord"><span class="mord mathnormal">a</span><span class="msupsub"><span class="vlist-t"><span class="vlist-r"><span class="vlist" style="height:0.8141em;"><span style="top:-3.063em;margin-right:0.05em;"><span class="pstrut" style="height:2.7em;"></span><span class="sizing reset-size6 size3 mtight"><span class="mord mtight">2</span></span></span></span></span></span></span></span><span class="mord mathnormal">b</span><span class="mspace" style="margin-right:0.2222em;"></span><span class="mbin">+</span><span class="mspace" style="margin-right:0.2222em;"></span></span><span class="base"><span class="strut" style="height:0.8974em;vertical-align:-0.0833em;"></span><span class="mord">3</span><span class="mord mathnormal">a</span><span class="mord"><span class="mord mathnormal">b</span><span class="msupsub"><span class="vlist-t"><span class="vlist-r"><span class="vlist" style="height:0.8141em;"><span style="top:-3.063em;margin-right:0.05em;"><span class="pstrut" style="height:2.7em;"></span><span class="sizing reset-size6 size3 mtight"><span class="mord mtight">2</span></span></span></span></span></span></span></span><span class="mspace" style="margin-right:0.2222em;"></span><span class="mbin">−</span><span class="mspace" style="margin-right:0.2222em;"></span></span><span class="base"><span class="strut" style="height:0.8141em;"></span><span class="mord"><span class="mord mathnormal">b</span><span class="msupsub"><span class="vlist-t"><span class="vlist-r"><span class="vlist" style="height:0.8141em;"><span style="top:-3.063em;margin-right:0.05em;"><span class="pstrut" style="height:2.7em;"></span><span class="sizing reset-size6 size3 mtight"><span class="mord mtight">3</span></span></span></span></span></span></span></span></span></span></span></span>với<span class="math-inline"><span class="katex"><span class="katex-mathml"><math xmlns="http://www.w3.org/1998/Math/MathML"><semantics><mrow><mi>a</mi><mo>=</mo><mn>2</mn></mrow><annotation encoding="application/x-tex">a=2</annotation></semantics></math></span><span class="katex-html" aria-hidden="true"><span class="base"><span class="strut" style="height:0.4306em;"></span><span class="mord mathnormal">a</span><span class="mspace" style="margin-right:0.2778em;"></span><span class="mrel">=</span><span class="mspace" style="margin-right:0.2778em;"></span></span><span class="base"><span class="strut" style="height:0.6444em;"></span><span class="mord">2</span></span></span></span></span>,<span class="math-inline"><span class="katex"><span class="katex-mathml"><math xmlns="http://www.w3.org/1998/Math/MathML"><semantics><mrow><mi>b</mi><mo>=</mo><mn>1</mn></mrow><annotation encoding="application/x-tex">b=1</annotation></semantics></math></span><span class="katex-html" aria-hidden="true"><span class="base"><span class="strut" style="height:0.6944em;"></span><span class="mord mathnormal">b</span><span class="mspace" style="margin-right:0.2778em;"></span><span class="mrel">=</span><span class="mspace" style="margin-right:0.2778em;"></span></span><span class="base"><span class="strut" style="height:0.6444em;"></span><span class="mord">1</span></span></span></span></span><!--LATEX_PROCESSED_1756993854716--></li><li><span class="math-inline"><span class="katex"><span class="katex-mathml"><math xmlns="http://www.w3.org/1998/Math/MathML"><semantics><mrow><msup><mn>2</mn><mn>3</mn></msup><mo>−</mo><mn>3</mn><mi>i</mi><mi>m</mi><mi>e</mi><mi>s</mi><msup><mn>2</mn><mn>2</mn></msup><mi>i</mi><mi>m</mi><mi>e</mi><mi>s</mi><mn>1</mn><mo>+</mo><mn>3</mn><mi>i</mi><mi>m</mi><mi>e</mi><mi>s</mi><mn>2</mn><mi>i</mi><mi>m</mi><mi>e</mi><mi>s</mi><msup><mn>1</mn><mn>2</mn></msup><mo>−</mo><msup><mn>1</mn><mn>3</mn></msup><mo>=</mo><mn>8</mn><mo>−</mo><mn>12</mn><mo>+</mo><mn>6</mn><mo>−</mo><mn>1</mn><mo>=</mo><mn>1</mn></mrow><annotation encoding="application/x-tex">2^3 - 3imes2^2imes1 + 3imes2imes1^2 - 1^3 = 8 - 12 + 6 - 1 = 1</annotation></semantics></math></span><span class="katex-html" aria-hidden="true"><span class="base"><span class="strut" style="height:0.8974em;vertical-align:-0.0833em;"></span><span class="mord"><span class="mord">2</span><span class="msupsub"><span class="vlist-t"><span class="vlist-r"><span class="vlist" style="height:0.8141em;"><span style="top:-3.063em;margin-right:0.05em;"><span class="pstrut" style="height:2.7em;"></span><span class="sizing reset-size6 size3 mtight"><span class="mord mtight">3</span></span></span></span></span></span></span></span><span class="mspace" style="margin-right:0.2222em;"></span><span class="mbin">−</span><span class="mspace" style="margin-right:0.2222em;"></span></span><span class="base"><span class="strut" style="height:0.8974em;vertical-align:-0.0833em;"></span><span class="mord">3</span><span class="mord mathnormal">im</span><span class="mord mathnormal">es</span><span class="mord"><span class="mord">2</span><span class="msupsub"><span class="vlist-t"><span class="vlist-r"><span class="vlist" style="height:0.8141em;"><span style="top:-3.063em;margin-right:0.05em;"><span class="pstrut" style="height:2.7em;"></span><span class="sizing reset-size6 size3 mtight"><span class="mord mtight">2</span></span></span></span></span></span></span></span><span class="mord mathnormal">im</span><span class="mord mathnormal">es</span><span class="mord">1</span><span class="mspace" style="margin-right:0.2222em;"></span><span class="mbin">+</span><span class="mspace" style="margin-right:0.2222em;"></span></span><span class="base"><span class="strut" style="height:0.8974em;vertical-align:-0.0833em;"></span><span class="mord">3</span><span class="mord mathnormal">im</span><span class="mord mathnormal">es</span><span class="mord">2</span><span class="mord mathnormal">im</span><span class="mord mathnormal">es</span><span class="mord"><span class="mord">1</span><span class="msupsub"><span class="vlist-t"><span class="vlist-r"><span class="vlist" style="height:0.8141em;"><span style="top:-3.063em;margin-right:0.05em;"><span class="pstrut" style="height:2.7em;"></span><span class="sizing reset-size6 size3 mtight"><span class="mord mtight">2</span></span></span></span></span></span></span></span><span class="mspace" style="margin-right:0.2222em;"></span><span class="mbin">−</span><span class="mspace" style="margin-right:0.2222em;"></span></span><span class="base"><span class="strut" style="height:0.8141em;"></span><span class="mord"><span class="mord">1</span><span class="msupsub"><span class="vlist-t"><span class="vlist-r"><span class="vlist" style="height:0.8141em;"><span style="top:-3.063em;margin-right:0.05em;"><span class="pstrut" style="height:2.7em;"></span><span class="sizing reset-size6 size3 mtight"><span class="mord mtight">3</span></span></span></span></span></span></span></span><span class="mspace" style="margin-right:0.2778em;"></span><span class="mrel">=</span><span class="mspace" style="margin-right:0.2778em;"></span></span><span class="base"><span class="strut" style="height:0.7278em;vertical-align:-0.0833em;"></span><span class="mord">8</span><span class="mspace" style="margin-right:0.2222em;"></span><span class="mbin">−</span><span class="mspace" style="margin-right:0.2222em;"></span></span><span class="base"><span class="strut" style="height:0.7278em;vertical-align:-0.0833em;"></span><span class="mord">12</span><span class="mspace" style="margin-right:0.2222em;"></span><span class="mbin">+</span><span class="mspace" style="margin-right:0.2222em;"></span></span><span class="base"><span class="strut" style="height:0.7278em;vertical-align:-0.0833em;"></span><span class="mord">6</span><span class="mspace" style="margin-right:0.2222em;"></span><span class="mbin">−</span><span class="mspace" style="margin-right:0.2222em;"></span></span><span class="base"><span class="strut" style="height:0.6444em;"></span><span class="mord">1</span><span class="mspace" style="margin-right:0.2778em;"></span><span class="mrel">=</span><span class="mspace" style="margin-right:0.2778em;"></span></span><span class="base"><span class="strut" style="height:0.6444em;"></span><span class="mord">1</span></span></span></span></span><!--LATEX_PROCESSED_1756993854718--></li></ul><p><strong>Lưu ý: Cẩn thận khi thay số, đừng quên dấu trừ!</strong></p><h2><strong>3.2 Ví dụ nâng cao</strong></h2><p><strong>Ví dụ: Rút gọn biểu thức<span class="math-inline"><span class="katex"><span class="katex-mathml"><math xmlns="http://www.w3.org/1998/Math/MathML"><semantics><mrow><mo stretchy="false">(</mo><mi>x</mi><mo>−</mo><mn>2</mn><mi>y</mi><msup><mo stretchy="false">)</mo><mn>3</mn></msup></mrow><annotation encoding="application/x-tex">(x-2y)^3</annotation></semantics></math></span><span class="katex-html" aria-hidden="true"><span class="base"><span class="strut" style="height:1em;vertical-align:-0.25em;"></span><span class="mopen">(</span><span class="mord mathnormal">x</span><span class="mspace" style="margin-right:0.2222em;"></span><span class="mbin">−</span><span class="mspace" style="margin-right:0.2222em;"></span></span><span class="base"><span class="strut" style="height:1.0641em;vertical-align:-0.25em;"></span><span class="mord">2</span><span class="mord mathnormal" style="margin-right:0.03588em;">y</span><span class="mclose"><span class="mclose">)</span><span class="msupsub"><span class="vlist-t"><span class="vlist-r"><span class="vlist" style="height:0.8141em;"><span style="top:-3.063em;margin-right:0.05em;"><span class="pstrut" style="height:2.7em;"></span><span class="sizing reset-size6 size3 mtight"><span class="mord mtight">3</span></span></span></span></span></span></span></span></span></span></span></span>.<!--LATEX_PROCESSED_1756993854718--></strong></p><p><em>Áp dụng công thức:</em></p><div class="math-block my-4 text-center"><div class="math-display" role="img" aria-label="Mathematical expression: < / d i v >< p > − < s t ro n g > C a ˊ c h g hinh ớ hi ệ u q u ả :< / s t ro n g > H a ~ y nh ớ đ u ˊ n g t h ứ t ự d a ^ ˊ u “ + , − , + , − ” v a ˋ l ư u y ˊ h ệ s o ^ ˊ 1 − 3 − 3 − 1 k e ˋ m t h eo l u ~ y t h ừ a g i ả m d a ^ ˋ n c ủ a < s p an c l a ss = " ma t h − in l in e " >< s p an c l a ss = " ka t e x " >< s p an c l a ss = " ka t e x − ma t hm l " >< ma t h x m l n s = " h ttp : // www . w 3. or g /1998/ M a t h / M a t h M L " >< se man t i cs >< m ro w >< mi > a < / mi >< / m ro w >< ann o t a t i o n e n co d in g = " a ppl i c a t i o n / x − t e x " > a < / ann o t a t i o n >< / se man t i cs >< / ma t h >< / s p an >< s p an c l a ss = " ka t e x − h t m l " a r ia − hi dd e n = " t r u e " >< s p an c l a ss = " ba se " >< s p an c l a ss = " s t r u t " s t y l e = " h e i g h t : 0.4306 e m ; " >< / s p an >< s p an c l a ss = " m or d ma t hn or ma l " > a < / s p an >< / s p an >< / s p an >< / s p an >< / s p an > v a ˋ t a ˘ n g d a ^ ˋ n c ủ a < s p an c l a ss = " ma t h − in l in e " >< s p an c l a ss = " ka t e x " >< s p an c l a ss = " ka t e x − ma t hm l " >< ma t h x m l n s = " h ttp : // www . w 3. or g /1998/ M a t h / M a t h M L " >< se man t i cs >< m ro w >< mi > b < / mi >< / m ro w >< ann o t a t i o n e n co d in g = " a ppl i c a t i o n / x − t e x " > b < / ann o t a t i o n >< / se man t i cs >< / ma t h >< / s p an >< s p an c l a ss = " ka t e x − h t m l " a r ia − hi dd e n = " t r u e " >< s p an c l a ss = " ba se " >< s p an c l a ss = " s t r u t " s t y l e = " h e i g h t : 0.6944 e m ; " >< / s p an >< s p an c l a ss = " m or d ma t hn or ma l " > b < / s p an >< / s p an >< / s p an >< / s p an >< / s p an > t ro n g t ừ n g h ạ n g t ử. < ! − − L A TE X P ROCESSE D 1 756993854712 − − >< / p >< p > − Đ i e ^ ˋ u ki ệ n s ử d ụ n g : C h ỉ s ử d ụ n g khihi ệ u ở c u ˋ n g d ạ n g < s p an c l a ss = " ma t h − in l in e " >< s p an c l a ss = " ka t e x " >< s p an c l a ss = " ka t e x − ma t hm l " >< ma t h x m l n s = " h ttp : // www . w 3. or g /1998/ M a t h / M a t h M L " >< se man t i cs >< m ro w >< m os t re t c h y = " f a l se " > ( < / m o >< mi > a < / mi >< m o > − < / m o >< mi > b < / mi >< m s u p >< m os t re t c h y = " f a l se " > ) < / m o >< mn > 3 < / mn >< / m s u p >< / m ro w >< ann o t a t i o n e n co d in g = " a ppl i c a t i o n / x − t e x " > ( a − b ) 3 < / ann o t a t i o n >< / se man t i cs >< / ma t h >< / s p an >< s p an c l a ss = " ka t e x − h t m l " a r ia − hi dd e n = " t r u e " >< s p an c l a ss = " ba se " >< s p an c l a ss = " s t r u t " s t y l e = " h e i g h t : 1 e m ; v er t i c a l − a l i g n : − 0.25 e m ; " >< / s p an >< s p an c l a ss = " m o p e n " > ( < / s p an >< s p an c l a ss = " m or d ma t hn or ma l " > a < / s p an >< s p an c l a ss = " m s p a ce " s t y l e = " ma r g in − r i g h t : 0.2222 e m ; " >< / s p an >< s p an c l a ss = " mbin " > − < / s p an >< s p an c l a ss = " m s p a ce " s t y l e = " ma r g in − r i g h t : 0.2222 e m ; " >< / s p an >< / s p an >< s p an c l a ss = " ba se " >< s p an c l a ss = " s t r u t " s t y l e = " h e i g h t : 1.0641 e m ; v er t i c a l − a l i g n : − 0.25 e m ; " >< / s p an >< s p an c l a ss = " m or d ma t hn or ma l " > b < / s p an >< s p an c l a ss = " m c l ose " >< s p an c l a ss = " m c l ose " > ) < / s p an >< s p an c l a ss = " m s u p s u b " >< s p an c l a ss = " v l i s t − t " >< s p an c l a ss = " v l i s t − r " >< s p an c l a ss = " v l i s t " s t y l e = " h e i g h t : 0.8141 e m ; " >< s p an s t y l e = " t o p : − 3.063 e m ; ma r g in − r i g h t : 0.05 e m ; " >< s p an c l a ss = " p s t r u t " s t y l e = " h e i g h t : 2.7 e m ; " >< / s p an >< s p an c l a ss = " s i z in g rese t − s i ze 6 s i ze 3 m t i g h t " >< s p an c l a ss = " m or d m t i g h t " > 3 < / s p an >< / s p an >< / s p an >< / s p an >< / s p an >< / s p an >< / s p an >< / s p an >< / s p an >< / s p an >< / s p an >< / s p an > . < ! − − L A TE X P ROCESSE D 1 756993854713 − − >< / p >< p > − B i e ^ ˊ n t h ể : D ạ n g t ổ n g q u a ˊ t h ơ n l a ˋ l ậ pp h ươ n g c ủ am ộ tt ổ n g < s p an c l a ss = " ma t h − in l in e " >< s p an c l a ss = " ka t e x " >< s p an c l a ss = " ka t e x − ma t hm l " >< ma t h x m l n s = " h ttp : // www . w 3. or g /1998/ M a t h / M a t h M L " >< se man t i cs >< m ro w >< m os t re t c h y = " f a l se " > ( < / m o >< mi > a < / mi >< m o > + < / m o >< mi > b < / mi >< m s u p >< m os t re t c h y = " f a l se " > ) < / m o >< mn > 3 < / mn >< / m s u p >< m o >=< / m o >< m s u p >< mi > a < / mi >< mn > 3 < / mn >< / m s u p >< m o > + < / m o >< mn > 3 < / mn >< m s u p >< mi > a < / mi >< mn > 2 < / mn >< / m s u p >< mi > b < / mi >< m o > + < / m o >< mn > 3 < / mn >< mi > a < / mi >< m s u p >< mi > b < / mi >< mn > 2 < / mn >< / m s u p >< m o > + < / m o >< m s u p >< mi > b < / mi >< mn > 3 < / mn >< / m s u p >< / m ro w >< ann o t a t i o n e n co d in g = " a ppl i c a t i o n / x − t e x " > ( a + b ) 3 = a 3 + 3 a 2 b + 3 a b 2 + b 3 < / ann o t a t i o n >< / se man t i cs >< / ma t h >< / s p an >< s p an c l a ss = " ka t e x − h t m l " a r ia − hi dd e n = " t r u e " >< s p an c l a ss = " ba se " >< s p an c l a ss = " s t r u t " s t y l e = " h e i g h t : 1 e m ; v er t i c a l − a l i g n : − 0.25 e m ; " >< / s p an >< s p an c l a ss = " m o p e n " > ( < / s p an >< s p an c l a ss = " m or d ma t hn or ma l " > a < / s p an >< s p an c l a ss = " m s p a ce " s t y l e = " ma r g in − r i g h t : 0.2222 e m ; " >< / s p an >< s p an c l a ss = " mbin " > + < / s p an >< s p an c l a ss = " m s p a ce " s t y l e = " ma r g in − r i g h t : 0.2222 e m ; " >< / s p an >< / s p an >< s p an c l a ss = " ba se " >< s p an c l a ss = " s t r u t " s t y l e = " h e i g h t : 1.0641 e m ; v er t i c a l − a l i g n : − 0.25 e m ; " >< / s p an >< s p an c l a ss = " m or d ma t hn or ma l " > b < / s p an >< s p an c l a ss = " m c l ose " >< s p an c l a ss = " m c l ose " > ) < / s p an >< s p an c l a ss = " m s u p s u b " >< s p an c l a ss = " v l i s t − t " >< s p an c l a ss = " v l i s t − r " >< s p an c l a ss = " v l i s t " s t y l e = " h e i g h t : 0.8141 e m ; " >< s p an s t y l e = " t o p : − 3.063 e m ; ma r g in − r i g h t : 0.05 e m ; " >< s p an c l a ss = " p s t r u t " s t y l e = " h e i g h t : 2.7 e m ; " >< / s p an >< s p an c l a ss = " s i z in g rese t − s i ze 6 s i ze 3 m t i g h t " >< s p an c l a ss = " m or d m t i g h t " > 3 < / s p an >< / s p an >< / s p an >< / s p an >< / s p an >< / s p an >< / s p an >< / s p an >< s p an c l a ss = " m s p a ce " s t y l e = " ma r g in − r i g h t : 0.2778 e m ; " >< / s p an >< s p an c l a ss = " m re l " >=< / s p an >< s p an c l a ss = " m s p a ce " s t y l e = " ma r g in − r i g h t : 0.2778 e m ; " >< / s p an >< / s p an >< s p an c l a ss = " ba se " >< s p an c l a ss = " s t r u t " s t y l e = " h e i g h t : 0.8974 e m ; v er t i c a l − a l i g n : − 0.0833 e m ; " >< / s p an >< s p an c l a ss = " m or d " >< s p an c l a ss = " m or d ma t hn or ma l " > a < / s p an >< s p an c l a ss = " m s u p s u b " >< s p an c l a ss = " v l i s t − t " >< s p an c l a ss = " v l i s t − r " >< s p an c l a ss = " v l i s t " s t y l e = " h e i g h t : 0.8141 e m ; " >< s p an s t y l e = " t o p : − 3.063 e m ; ma r g in − r i g h t : 0.05 e m ; " >< s p an c l a ss = " p s t r u t " s t y l e = " h e i g h t : 2.7 e m ; " >< / s p an >< s p an c l a ss = " s i z in g rese t − s i ze 6 s i ze 3 m t i g h t " >< s p an c l a ss = " m or d m t i g h t " > 3 < / s p an >< / s p an >< / s p an >< / s p an >< / s p an >< / s p an >< / s p an >< / s p an >< s p an c l a ss = " m s p a ce " s t y l e = " ma r g in − r i g h t : 0.2222 e m ; " >< / s p an >< s p an c l a ss = " mbin " > + < / s p an >< s p an c l a ss = " m s p a ce " s t y l e = " ma r g in − r i g h t : 0.2222 e m ; " >< / s p an >< / s p an >< s p an c l a ss = " ba se " >< s p an c l a ss = " s t r u t " s t y l e = " h e i g h t : 0.8974 e m ; v er t i c a l − a l i g n : − 0.0833 e m ; " >< / s p an >< s p an c l a ss = " m or d " > 3 < / s p an >< s p an c l a ss = " m or d " >< s p an c l a ss = " m or d ma t hn or ma l " > a < / s p an >< s p an c l a ss = " m s u p s u b " >< s p an c l a ss = " v l i s t − t " >< s p an c l a ss = " v l i s t − r " >< s p an c l a ss = " v l i s t " s t y l e = " h e i g h t : 0.8141 e m ; " >< s p an s t y l e = " t o p : − 3.063 e m ; ma r g in − r i g h t : 0.05 e m ; " >< s p an c l a ss = " p s t r u t " s t y l e = " h e i g h t : 2.7 e m ; " >< / s p an >< s p an c l a ss = " s i z in g rese t − s i ze 6 s i ze 3 m t i g h t " >< s p an c l a ss = " m or d m t i g h t " > 2 < / s p an >< / s p an >< / s p an >< / s p an >< / s p an >< / s p an >< / s p an >< / s p an >< s p an c l a ss = " m or d ma t hn or ma l " > b < / s p an >< s p an c l a ss = " m s p a ce " s t y l e = " ma r g in − r i g h t : 0.2222 e m ; " >< / s p an >< s p an c l a ss = " mbin " > + < / s p an >< s p an c l a ss = " m s p a ce " s t y l e = " ma r g in − r i g h t : 0.2222 e m ; " >< / s p an >< / s p an >< s p an c l a ss = " ba se " >< s p an c l a ss = " s t r u t " s t y l e = " h e i g h t : 0.8974 e m ; v er t i c a l − a l i g n : − 0.0833 e m ; " >< / s p an >< s p an c l a ss = " m or d " > 3 < / s p an >< s p an c l a ss = " m or d ma t hn or ma l " > a < / s p an >< s p an c l a ss = " m or d " >< s p an c l a ss = " m or d ma t hn or ma l " > b < / s p an >< s p an c l a ss = " m s u p s u b " >< s p an c l a ss = " v l i s t − t " >< s p an c l a ss = " v l i s t − r " >< s p an c l a ss = " v l i s t " s t y l e = " h e i g h t : 0.8141 e m ; " >< s p an s t y l e = " t o p : − 3.063 e m ; ma r g in − r i g h t : 0.05 e m ; " >< s p an c l a ss = " p s t r u t " s t y l e = " h e i g h t : 2.7 e m ; " >< / s p an >< s p an c l a ss = " s i z in g rese t − s i ze 6 s i ze 3 m t i g h t " >< s p an c l a ss = " m or d m t i g h t " > 2 < / s p an >< / s p an >< / s p an >< / s p an >< / s p an >< / s p an >< / s p an >< / s p an >< s p an c l a ss = " m s p a ce " s t y l e = " ma r g in − r i g h t : 0.2222 e m ; " >< / s p an >< s p an c l a ss = " mbin " > + < / s p an >< s p an c l a ss = " m s p a ce " s t y l e = " ma r g in − r i g h t : 0.2222 e m ; " >< / s p an >< / s p an >< s p an c l a ss = " ba se " >< s p an c l a ss = " s t r u t " s t y l e = " h e i g h t : 0.8141 e m ; " >< / s p an >< s p an c l a ss = " m or d " >< s p an c l a ss = " m or d ma t hn or ma l " > b < / s p an >< s p an c l a ss = " m s u p s u b " >< s p an c l a ss = " v l i s t − t " >< s p an c l a ss = " v l i s t − r " >< s p an c l a ss = " v l i s t " s t y l e = " h e i g h t : 0.8141 e m ; " >< s p an s t y l e = " t o p : − 3.063 e m ; ma r g in − r i g h t : 0.05 e m ; " >< s p an c l a ss = " p s t r u t " s t y l e = " h e i g h t : 2.7 e m ; " >< / s p an >< s p an c l a ss = " s i z in g rese t − s i ze 6 s i ze 3 m t i g h t " >< s p an c l a ss = " m or d m t i g h t " > 3 < / s p an >< / s p an >< / s p an >< / s p an >< / s p an >< / s p an >< / s p an >< / s p an >< / s p an >< / s p an >< / s p an >< / s p an > . < ! − − L A TE X P ROCESSE D 1 756993854714 − − >< / p >< h 2 >< s t ro n g > 3. V ı ˊ d ụ minhh ọ a c hi t i e ^ ˊ t < / s t ro n g >< / h 2 >< h 2 >< s t ro n g > 3.1 V ı ˊ d ụ c ơ b ả n < / s t ro n g >< / h 2 >< p >< s t ro n g > V ı ˊ d ụ : T ı ˊ nh < s p an c l a ss = " ma t h − in l in e " >< s p an c l a ss = " ka t e x " >< s p an c l a ss = " ka t e x − ma t hm l " >< ma t h x m l n s = " h ttp : // www . w 3. or g /1998/ M a t h / M a t h M L " >< se man t i cs >< m ro w >< m os t re t c h y = " f a l se " > ( < / m o >< mn > 2 < / mn >< m o > − < / m o >< mn > 1 < / mn >< m s u p >< m os t re t c h y = " f a l se " > ) < / m o >< mn > 3 < / mn >< / m s u p >< / m ro w >< ann o t a t i o n e n co d in g = " a ppl i c a t i o n / x − t e x " > ( 2 − 1 ) 3 < / ann o t a t i o n >< / se man t i cs >< / ma t h >< / s p an >< s p an c l a ss = " ka t e x − h t m l " a r ia − hi dd e n = " t r u e " >< s p an c l a ss = " ba se " >< s p an c l a ss = " s t r u t " s t y l e = " h e i g h t : 1 e m ; v er t i c a l − a l i g n : − 0.25 e m ; " >< / s p an >< s p an c l a ss = " m o p e n " > ( < / s p an >< s p an c l a ss = " m or d " > 2 < / s p an >< s p an c l a ss = " m s p a ce " s t y l e = " ma r g in − r i g h t : 0.2222 e m ; " >< / s p an >< s p an c l a ss = " mbin " > − < / s p an >< s p an c l a ss = " m s p a ce " s t y l e = " ma r g in − r i g h t : 0.2222 e m ; " >< / s p an >< / s p an >< s p an c l a ss = " ba se " >< s p an c l a ss = " s t r u t " s t y l e = " h e i g h t : 1.0641 e m ; v er t i c a l − a l i g n : − 0.25 e m ; " >< / s p an >< s p an c l a ss = " m or d " > 1 < / s p an >< s p an c l a ss = " m c l ose " >< s p an c l a ss = " m c l ose " > ) < / s p an >< s p an c l a ss = " m s u p s u b " >< s p an c l a ss = " v l i s t − t " >< s p an c l a ss = " v l i s t − r " >< s p an c l a ss = " v l i s t " s t y l e = " h e i g h t : 0.8141 e m ; " >< s p an s t y l e = " t o p : − 3.063 e m ; ma r g in − r i g h t : 0.05 e m ; " >< s p an c l a ss = " p s t r u t " s t y l e = " h e i g h t : 2.7 e m ; " >< / s p an >< s p an c l a ss = " s i z in g rese t − s i ze 6 s i ze 3 m t i g h t " >< s p an c l a ss = " m or d m t i g h t " > 3 < / s p an >< / s p an >< / s p an >< / s p an >< / s p an >< / s p an >< / s p an >< / s p an >< / s p an >< / s p an >< / s p an >< / s p an > . < ! − − L A TE X P ROCESSE D 1 756993854715 − − >< / s t ro n g >< / p >< p >< e m > G i ả i t ừ n g b ư ớ c :< / e m >< / p >< u l >< l i > A ˊ p d ụ n g c o ^ n g t h ứ c :< s p an c l a ss = " ma t h − in l in e " >< s p an c l a ss = " ka t e x " >< s p an c l a ss = " ka t e x − ma t hm l " >< ma t h x m l n s = " h ttp : // www . w 3. or g /1998/ M a t h / M a t h M L " >< se man t i cs >< m ro w >< m os t re t c h y = " f a l se " > ( < / m o >< mi > a < / mi >< m o > − < / m o >< mi > b < / mi >< m s u p >< m os t re t c h y = " f a l se " > ) < / m o >< mn > 3 < / mn >< / m s u p >< m o >=< / m o >< m s u p >< mi > a < / mi >< mn > 3 < / mn >< / m s u p >< m o > − < / m o >< mn > 3 < / mn >< m s u p >< mi > a < / mi >< mn > 2 < / mn >< / m s u p >< mi > b < / mi >< m o > + < / m o >< mn > 3 < / mn >< mi > a < / mi >< m s u p >< mi > b < / mi >< mn > 2 < / mn >< / m s u p >< m o > − < / m o >< m s u p >< mi > b < / mi >< mn > 3 < / mn >< / m s u p >< / m ro w >< ann o t a t i o n e n co d in g = " a ppl i c a t i o n / x − t e x " > ( a − b ) 3 = a 3 − 3 a 2 b + 3 a b 2 − b 3 < / ann o t a t i o n >< / se man t i cs >< / ma t h >< / s p an >< s p an c l a ss = " ka t e x − h t m l " a r ia − hi dd e n = " t r u e " >< s p an c l a ss = " ba se " >< s p an c l a ss = " s t r u t " s t y l e = " h e i g h t : 1 e m ; v er t i c a l − a l i g n : − 0.25 e m ; " >< / s p an >< s p an c l a ss = " m o p e n " > ( < / s p an >< s p an c l a ss = " m or d ma t hn or ma l " > a < / s p an >< s p an c l a ss = " m s p a ce " s t y l e = " ma r g in − r i g h t : 0.2222 e m ; " >< / s p an >< s p an c l a ss = " mbin " > − < / s p an >< s p an c l a ss = " m s p a ce " s t y l e = " ma r g in − r i g h t : 0.2222 e m ; " >< / s p an >< / s p an >< s p an c l a ss = " ba se " >< s p an c l a ss = " s t r u t " s t y l e = " h e i g h t : 1.0641 e m ; v er t i c a l − a l i g n : − 0.25 e m ; " >< / s p an >< s p an c l a ss = " m or d ma t hn or ma l " > b < / s p an >< s p an c l a ss = " m c l ose " >< s p an c l a ss = " m c l ose " > ) < / s p an >< s p an c l a ss = " m s u p s u b " >< s p an c l a ss = " v l i s t − t " >< s p an c l a ss = " v l i s t − r " >< s p an c l a ss = " v l i s t " s t y l e = " h e i g h t : 0.8141 e m ; " >< s p an s t y l e = " t o p : − 3.063 e m ; ma r g in − r i g h t : 0.05 e m ; " >< s p an c l a ss = " p s t r u t " s t y l e = " h e i g h t : 2.7 e m ; " >< / s p an >< s p an c l a ss = " s i z in g rese t − s i ze 6 s i ze 3 m t i g h t " >< s p an c l a ss = " m or d m t i g h t " > 3 < / s p an >< / s p an >< / s p an >< / s p an >< / s p an >< / s p an >< / s p an >< / s p an >< s p an c l a ss = " m s p a ce " s t y l e = " ma r g in − r i g h t : 0.2778 e m ; " >< / s p an >< s p an c l a ss = " m re l " >=< / s p an >< s p an c l a ss = " m s p a ce " s t y l e = " ma r g in − r i g h t : 0.2778 e m ; " >< / s p an >< / s p an >< s p an c l a ss = " ba se " >< s p an c l a ss = " s t r u t " s t y l e = " h e i g h t : 0.8974 e m ; v er t i c a l − a l i g n : − 0.0833 e m ; " >< / s p an >< s p an c l a ss = " m or d " >< s p an c l a ss = " m or d ma t hn or ma l " > a < / s p an >< s p an c l a ss = " m s u p s u b " >< s p an c l a ss = " v l i s t − t " >< s p an c l a ss = " v l i s t − r " >< s p an c l a ss = " v l i s t " s t y l e = " h e i g h t : 0.8141 e m ; " >< s p an s t y l e = " t o p : − 3.063 e m ; ma r g in − r i g h t : 0.05 e m ; " >< s p an c l a ss = " p s t r u t " s t y l e = " h e i g h t : 2.7 e m ; " >< / s p an >< s p an c l a ss = " s i z in g rese t − s i ze 6 s i ze 3 m t i g h t " >< s p an c l a ss = " m or d m t i g h t " > 3 < / s p an >< / s p an >< / s p an >< / s p an >< / s p an >< / s p an >< / s p an >< / s p an >< s p an c l a ss = " m s p a ce " s t y l e = " ma r g in − r i g h t : 0.2222 e m ; " >< / s p an >< s p an c l a ss = " mbin " > − < / s p an >< s p an c l a ss = " m s p a ce " s t y l e = " ma r g in − r i g h t : 0.2222 e m ; " >< / s p an >< / s p an >< s p an c l a ss = " ba se " >< s p an c l a ss = " s t r u t " s t y l e = " h e i g h t : 0.8974 e m ; v er t i c a l − a l i g n : − 0.0833 e m ; " >< / s p an >< s p an c l a ss = " m or d " > 3 < / s p an >< s p an c l a ss = " m or d " >< s p an c l a ss = " m or d ma t hn or ma l " > a < / s p an >< s p an c l a ss = " m s u p s u b " >< s p an c l a ss = " v l i s t − t " >< s p an c l a ss = " v l i s t − r " >< s p an c l a ss = " v l i s t " s t y l e = " h e i g h t : 0.8141 e m ; " >< s p an s t y l e = " t o p : − 3.063 e m ; ma r g in − r i g h t : 0.05 e m ; " >< s p an c l a ss = " p s t r u t " s t y l e = " h e i g h t : 2.7 e m ; " >< / s p an >< s p an c l a ss = " s i z in g rese t − s i ze 6 s i ze 3 m t i g h t " >< s p an c l a ss = " m or d m t i g h t " > 2 < / s p an >< / s p an >< / s p an >< / s p an >< / s p an >< / s p an >< / s p an >< / s p an >< s p an c l a ss = " m or d ma t hn or ma l " > b < / s p an >< s p an c l a ss = " m s p a ce " s t y l e = " ma r g in − r i g h t : 0.2222 e m ; " >< / s p an >< s p an c l a ss = " mbin " > + < / s p an >< s p an c l a ss = " m s p a ce " s t y l e = " ma r g in − r i g h t : 0.2222 e m ; " >< / s p an >< / s p an >< s p an c l a ss = " ba se " >< s p an c l a ss = " s t r u t " s t y l e = " h e i g h t : 0.8974 e m ; v er t i c a l − a l i g n : − 0.0833 e m ; " >< / s p an >< s p an c l a ss = " m or d " > 3 < / s p an >< s p an c l a ss = " m or d ma t hn or ma l " > a < / s p an >< s p an c l a ss = " m or d " >< s p an c l a ss = " m or d ma t hn or ma l " > b < / s p an >< s p an c l a ss = " m s u p s u b " >< s p an c l a ss = " v l i s t − t " >< s p an c l a ss = " v l i s t − r " >< s p an c l a ss = " v l i s t " s t y l e = " h e i g h t : 0.8141 e m ; " >< s p an s t y l e = " t o p : − 3.063 e m ; ma r g in − r i g h t : 0.05 e m ; " >< s p an c l a ss = " p s t r u t " s t y l e = " h e i g h t : 2.7 e m ; " >< / s p an >< s p an c l a ss = " s i z in g rese t − s i ze 6 s i ze 3 m t i g h t " >< s p an c l a ss = " m or d m t i g h t " > 2 < / s p an >< / s p an >< / s p an >< / s p an >< / s p an >< / s p an >< / s p an >< / s p an >< s p an c l a ss = " m s p a ce " s t y l e = " ma r g in − r i g h t : 0.2222 e m ; " >< / s p an >< s p an c l a ss = " mbin " > − < / s p an >< s p an c l a ss = " m s p a ce " s t y l e = " ma r g in − r i g h t : 0.2222 e m ; " >< / s p an >< / s p an >< s p an c l a ss = " ba se " >< s p an c l a ss = " s t r u t " s t y l e = " h e i g h t : 0.8141 e m ; " >< / s p an >< s p an c l a ss = " m or d " >< s p an c l a ss = " m or d ma t hn or ma l " > b < / s p an >< s p an c l a ss = " m s u p s u b " >< s p an c l a ss = " v l i s t − t " >< s p an c l a ss = " v l i s t − r " >< s p an c l a ss = " v l i s t " s t y l e = " h e i g h t : 0.8141 e m ; " >< s p an s t y l e = " t o p : − 3.063 e m ; ma r g in − r i g h t : 0.05 e m ; " >< s p an c l a ss = " p s t r u t " s t y l e = " h e i g h t : 2.7 e m ; " >< / s p an >< s p an c l a ss = " s i z in g rese t − s i ze 6 s i ze 3 m t i g h t " >< s p an c l a ss = " m or d m t i g h t " > 3 < / s p an >< / s p an >< / s p an >< / s p an >< / s p an >< / s p an >< / s p an >< / s p an >< / s p an >< / s p an >< / s p an >< / s p an > v ớ i < s p an c l a ss = " ma t h − in l in e " >< s p an c l a ss = " ka t e x " >< s p an c l a ss = " ka t e x − ma t hm l " >< ma t h x m l n s = " h ttp : // www . w 3. or g /1998/ M a t h / M a t h M L " >< se man t i cs >< m ro w >< mi > a < / mi >< m o >=< / m o >< mn > 2 < / mn >< / m ro w >< ann o t a t i o n e n co d in g = " a ppl i c a t i o n / x − t e x " > a = 2 < / ann o t a t i o n >< / se man t i cs >< / ma t h >< / s p an >< s p an c l a ss = " ka t e x − h t m l " a r ia − hi dd e n = " t r u e " >< s p an c l a ss = " ba se " >< s p an c l a ss = " s t r u t " s t y l e = " h e i g h t : 0.4306 e m ; " >< / s p an >< s p an c l a ss = " m or d ma t hn or ma l " > a < / s p an >< s p an c l a ss = " m s p a ce " s t y l e = " ma r g in − r i g h t : 0.2778 e m ; " >< / s p an >< s p an c l a ss = " m re l " >=< / s p an >< s p an c l a ss = " m s p a ce " s t y l e = " ma r g in − r i g h t : 0.2778 e m ; " >< / s p an >< / s p an >< s p an c l a ss = " ba se " >< s p an c l a ss = " s t r u t " s t y l e = " h e i g h t : 0.6444 e m ; " >< / s p an >< s p an c l a ss = " m or d " > 2 < / s p an >< / s p an >< / s p an >< / s p an >< / s p an > , < s p an c l a ss = " ma t h − in l in e " >< s p an c l a ss = " ka t e x " >< s p an c l a ss = " ka t e x − ma t hm l " >< ma t h x m l n s = " h ttp : // www . w 3. or g /1998/ M a t h / M a t h M L " >< se man t i cs >< m ro w >< mi > b < / mi >< m o >=< / m o >< mn > 1 < / mn >< / m ro w >< ann o t a t i o n e n co d in g = " a ppl i c a t i o n / x − t e x " > b = 1 < / ann o t a t i o n >< / se man t i cs >< / ma t h >< / s p an >< s p an c l a ss = " ka t e x − h t m l " a r ia − hi dd e n = " t r u e " >< s p an c l a ss = " ba se " >< s p an c l a ss = " s t r u t " s t y l e = " h e i g h t : 0.6944 e m ; " >< / s p an >< s p an c l a ss = " m or d ma t hn or ma l " > b < / s p an >< s p an c l a ss = " m s p a ce " s t y l e = " ma r g in − r i g h t : 0.2778 e m ; " >< / s p an >< s p an c l a ss = " m re l " >=< / s p an >< s p an c l a ss = " m s p a ce " s t y l e = " ma r g in − r i g h t : 0.2778 e m ; " >< / s p an >< / s p an >< s p an c l a ss = " ba se " >< s p an c l a ss = " s t r u t " s t y l e = " h e i g h t : 0.6444 e m ; " >< / s p an >< s p an c l a ss = " m or d " > 1 < / s p an >< / s p an >< / s p an >< / s p an >< / s p an >< ! − − L A TE X P ROCESSE D 1 756993854716 − − >< / l i >< l i >< s p an c l a ss = " ma t h − in l in e " >< s p an c l a ss = " ka t e x " >< s p an c l a ss = " ka t e x − ma t hm l " >< ma t h x m l n s = " h ttp : // www . w 3. or g /1998/ M a t h / M a t h M L " >< se man t i cs >< m ro w >< m s u p >< mn > 2 < / mn >< mn > 3 < / mn >< / m s u p >< m o > − < / m o >< mn > 3 < / mn >< mi > i < / mi >< mi > m < / mi >< mi > e < / mi >< mi > s < / mi >< m s u p >< mn > 2 < / mn >< mn > 2 < / mn >< / m s u p >< mi > i < / mi >< mi > m < / mi >< mi > e < / mi >< mi > s < / mi >< mn > 1 < / mn >< m o > + < / m o >< mn > 3 < / mn >< mi > i < / mi >< mi > m < / mi >< mi > e < / mi >< mi > s < / mi >< mn > 2 < / mn >< mi > i < / mi >< mi > m < / mi >< mi > e < / mi >< mi > s < / mi >< m s u p >< mn > 1 < / mn >< mn > 2 < / mn >< / m s u p >< m o > − < / m o >< m s u p >< mn > 1 < / mn >< mn > 3 < / mn >< / m s u p >< m o >=< / m o >< mn > 8 < / mn >< m o > − < / m o >< mn > 12 < / mn >< m o > + < / m o >< mn > 6 < / mn >< m o > − < / m o >< mn > 1 < / mn >< m o >=< / m o >< mn > 1 < / mn >< / m ro w >< ann o t a t i o n e n co d in g = " a ppl i c a t i o n / x − t e x " > 2 3 − 3 im es 2 2 im es 1 + 3 im es 2 im es 1 2 − 1 3 = 8 − 12 + 6 − 1 = 1 < / ann o t a t i o n >< / se man t i cs >< / ma t h >< / s p an >< s p an c l a ss = " ka t e x − h t m l " a r ia − hi dd e n = " t r u e " >< s p an c l a ss = " ba se " >< s p an c l a ss = " s t r u t " s t y l e = " h e i g h t : 0.8974 e m ; v er t i c a l − a l i g n : − 0.0833 e m ; " >< / s p an >< s p an c l a ss = " m or d " >< s p an c l a ss = " m or d " > 2 < / s p an >< s p an c l a ss = " m s u p s u b " >< s p an c l a ss = " v l i s t − t " >< s p an c l a ss = " v l i s t − r " >< s p an c l a ss = " v l i s t " s t y l e = " h e i g h t : 0.8141 e m ; " >< s p an s t y l e = " t o p : − 3.063 e m ; ma r g in − r i g h t : 0.05 e m ; " >< s p an c l a ss = " p s t r u t " s t y l e = " h e i g h t : 2.7 e m ; " >< / s p an >< s p an c l a ss = " s i z in g rese t − s i ze 6 s i ze 3 m t i g h t " >< s p an c l a ss = " m or d m t i g h t " > 3 < / s p an >< / s p an >< / s p an >< / s p an >< / s p an >< / s p an >< / s p an >< / s p an >< s p an c l a ss = " m s p a ce " s t y l e = " ma r g in − r i g h t : 0.2222 e m ; " >< / s p an >< s p an c l a ss = " mbin " > − < / s p an >< s p an c l a ss = " m s p a ce " s t y l e = " ma r g in − r i g h t : 0.2222 e m ; " >< / s p an >< / s p an >< s p an c l a ss = " ba se " >< s p an c l a ss = " s t r u t " s t y l e = " h e i g h t : 0.8974 e m ; v er t i c a l − a l i g n : − 0.0833 e m ; " >< / s p an >< s p an c l a ss = " m or d " > 3 < / s p an >< s p an c l a ss = " m or d ma t hn or ma l " > im < / s p an >< s p an c l a ss = " m or d ma t hn or ma l " > es < / s p an >< s p an c l a ss = " m or d " >< s p an c l a ss = " m or d " > 2 < / s p an >< s p an c l a ss = " m s u p s u b " >< s p an c l a ss = " v l i s t − t " >< s p an c l a ss = " v l i s t − r " >< s p an c l a ss = " v l i s t " s t y l e = " h e i g h t : 0.8141 e m ; " >< s p an s t y l e = " t o p : − 3.063 e m ; ma r g in − r i g h t : 0.05 e m ; " >< s p an c l a ss = " p s t r u t " s t y l e = " h e i g h t : 2.7 e m ; " >< / s p an >< s p an c l a ss = " s i z in g rese t − s i ze 6 s i ze 3 m t i g h t " >< s p an c l a ss = " m or d m t i g h t " > 2 < / s p an >< / s p an >< / s p an >< / s p an >< / s p an >< / s p an >< / s p an >< / s p an >< s p an c l a ss = " m or d ma t hn or ma l " > im < / s p an >< s p an c l a ss = " m or d ma t hn or ma l " > es < / s p an >< s p an c l a ss = " m or d " > 1 < / s p an >< s p an c l a ss = " m s p a ce " s t y l e = " ma r g in − r i g h t : 0.2222 e m ; " >< / s p an >< s p an c l a ss = " mbin " > + < / s p an >< s p an c l a ss = " m s p a ce " s t y l e = " ma r g in − r i g h t : 0.2222 e m ; " >< / s p an >< / s p an >< s p an c l a ss = " ba se " >< s p an c l a ss = " s t r u t " s t y l e = " h e i g h t : 0.8974 e m ; v er t i c a l − a l i g n : − 0.0833 e m ; " >< / s p an >< s p an c l a ss = " m or d " > 3 < / s p an >< s p an c l a ss = " m or d ma t hn or ma l " > im < / s p an >< s p an c l a ss = " m or d ma t hn or ma l " > es < / s p an >< s p an c l a ss = " m or d " > 2 < / s p an >< s p an c l a ss = " m or d ma t hn or ma l " > im < / s p an >< s p an c l a ss = " m or d ma t hn or ma l " > es < / s p an >< s p an c l a ss = " m or d " >< s p an c l a ss = " m or d " > 1 < / s p an >< s p an c l a ss = " m s u p s u b " >< s p an c l a ss = " v l i s t − t " >< s p an c l a ss = " v l i s t − r " >< s p an c l a ss = " v l i s t " s t y l e = " h e i g h t : 0.8141 e m ; " >< s p an s t y l e = " t o p : − 3.063 e m ; ma r g in − r i g h t : 0.05 e m ; " >< s p an c l a ss = " p s t r u t " s t y l e = " h e i g h t : 2.7 e m ; " >< / s p an >< s p an c l a ss = " s i z in g rese t − s i ze 6 s i ze 3 m t i g h t " >< s p an c l a ss = " m or d m t i g h t " > 2 < / s p an >< / s p an >< / s p an >< / s p an >< / s p an >< / s p an >< / s p an >< / s p an >< s p an c l a ss = " m s p a ce " s t y l e = " ma r g in − r i g h t : 0.2222 e m ; " >< / s p an >< s p an c l a ss = " mbin " > − < / s p an >< s p an c l a ss = " m s p a ce " s t y l e = " ma r g in − r i g h t : 0.2222 e m ; " >< / s p an >< / s p an >< s p an c l a ss = " ba se " >< s p an c l a ss = " s t r u t " s t y l e = " h e i g h t : 0.8141 e m ; " >< / s p an >< s p an c l a ss = " m or d " >< s p an c l a ss = " m or d " > 1 < / s p an >< s p an c l a ss = " m s u p s u b " >< s p an c l a ss = " v l i s t − t " >< s p an c l a ss = " v l i s t − r " >< s p an c l a ss = " v l i s t " s t y l e = " h e i g h t : 0.8141 e m ; " >< s p an s t y l e = " t o p : − 3.063 e m ; ma r g in − r i g h t : 0.05 e m ; " >< s p an c l a ss = " p s t r u t " s t y l e = " h e i g h t : 2.7 e m ; " >< / s p an >< s p an c l a ss = " s i z in g rese t − s i ze 6 s i ze 3 m t i g h t " >< s p an c l a ss = " m or d m t i g h t " > 3 < / s p an >< / s p an >< / s p an >< / s p an >< / s p an >< / s p an >< / s p an >< / s p an >< s p an c l a ss = " m s p a ce " s t y l e = " ma r g in − r i g h t : 0.2778 e m ; " >< / s p an >< s p an c l a ss = " m re l " >=< / s p an >< s p an c l a ss = " m s p a ce " s t y l e = " ma r g in − r i g h t : 0.2778 e m ; " >< / s p an >< / s p an >< s p an c l a ss = " ba se " >< s p an c l a ss = " s t r u t " s t y l e = " h e i g h t : 0.7278 e m ; v er t i c a l − a l i g n : − 0.0833 e m ; " >< / s p an >< s p an c l a ss = " m or d " > 8 < / s p an >< s p an c l a ss = " m s p a ce " s t y l e = " ma r g in − r i g h t : 0.2222 e m ; " >< / s p an >< s p an c l a ss = " mbin " > − < / s p an >< s p an c l a ss = " m s p a ce " s t y l e = " ma r g in − r i g h t : 0.2222 e m ; " >< / s p an >< / s p an >< s p an c l a ss = " ba se " >< s p an c l a ss = " s t r u t " s t y l e = " h e i g h t : 0.7278 e m ; v er t i c a l − a l i g n : − 0.0833 e m ; " >< / s p an >< s p an c l a ss = " m or d " > 12 < / s p an >< s p an c l a ss = " m s p a ce " s t y l e = " ma r g in − r i g h t : 0.2222 e m ; " >< / s p an >< s p an c l a ss = " mbin " > + < / s p an >< s p an c l a ss = " m s p a ce " s t y l e = " ma r g in − r i g h t : 0.2222 e m ; " >< / s p an >< / s p an >< s p an c l a ss = " ba se " >< s p an c l a ss = " s t r u t " s t y l e = " h e i g h t : 0.7278 e m ; v er t i c a l − a l i g n : − 0.0833 e m ; " >< / s p an >< s p an c l a ss = " m or d " > 6 < / s p an >< s p an c l a ss = " m s p a ce " s t y l e = " ma r g in − r i g h t : 0.2222 e m ; " >< / s p an >< s p an c l a ss = " mbin " > − < / s p an >< s p an c l a ss = " m s p a ce " s t y l e = " ma r g in − r i g h t : 0.2222 e m ; " >< / s p an >< / s p an >< s p an c l a ss = " ba se " >< s p an c l a ss = " s t r u t " s t y l e = " h e i g h t : 0.6444 e m ; " >< / s p an >< s p an c l a ss = " m or d " > 1 < / s p an >< s p an c l a ss = " m s p a ce " s t y l e = " ma r g in − r i g h t : 0.2778 e m ; " >< / s p an >< s p an c l a ss = " m re l " >=< / s p an >< s p an c l a ss = " m s p a ce " s t y l e = " ma r g in − r i g h t : 0.2778 e m ; " >< / s p an >< / s p an >< s p an c l a ss = " ba se " >< s p an c l a ss = " s t r u t " s t y l e = " h e i g h t : 0.6444 e m ; " >< / s p an >< s p an c l a ss = " m or d " > 1 < / s p an >< / s p an >< / s p an >< / s p an >< / s p an >< ! − − L A TE X P ROCESSE D 1 756993854718 − − >< / l i >< / u l >< p >< s t ro n g > L ư u y ˊ : C ẩ n t h ậ nkhi t ha ys o ^ ˊ , đ ừ n g q u e ^ n d a ^ ˊ u t r ừ ! < / s t ro n g >< / p >< h 2 >< s t ro n g > 3.2 V ı ˊ d ụ n a ^ n g c a o < / s t ro n g >< / h 2 >< p >< s t ro n g > V ı ˊ d ụ : R u ˊ t g ọ nbi ể u t h ứ c < s p an c l a ss = " ma t h − in l in e " >< s p an c l a ss = " ka t e x " >< s p an c l a ss = " ka t e x − ma t hm l " >< ma t h x m l n s = " h ttp : // www . w 3. or g /1998/ M a t h / M a t h M L " >< se man t i cs >< m ro w >< m os t re t c h y = " f a l se " > ( < / m o >< mi > x < / mi >< m o > − < / m o >< mn > 2 < / mn >< mi > y < / mi >< m s u p >< m os t re t c h y = " f a l se " > ) < / m o >< mn > 3 < / mn >< / m s u p >< / m ro w >< ann o t a t i o n e n co d in g = " a ppl i c a t i o n / x − t e x " > ( x − 2 y ) 3 < / ann o t a t i o n >< / se man t i cs >< / ma t h >< / s p an >< s p an c l a ss = " ka t e x − h t m l " a r ia − hi dd e n = " t r u e " >< s p an c l a ss = " ba se " >< s p an c l a ss = " s t r u t " s t y l e = " h e i g h t : 1 e m ; v er t i c a l − a l i g n : − 0.25 e m ; " >< / s p an >< s p an c l a ss = " m o p e n " > ( < / s p an >< s p an c l a ss = " m or d ma t hn or ma l " > x < / s p an >< s p an c l a ss = " m s p a ce " s t y l e = " ma r g in − r i g h t : 0.2222 e m ; " >< / s p an >< s p an c l a ss = " mbin " > − < / s p an >< s p an c l a ss = " m s p a ce " s t y l e = " ma r g in − r i g h t : 0.2222 e m ; " >< / s p an >< / s p an >< s p an c l a ss = " ba se " >< s p an c l a ss = " s t r u t " s t y l e = " h e i g h t : 1.0641 e m ; v er t i c a l − a l i g n : − 0.25 e m ; " >< / s p an >< s p an c l a ss = " m or d " > 2 < / s p an >< s p an c l a ss = " m or d ma t hn or ma l " s t y l e = " ma r g in − r i g h t : 0.03588 e m ; " > y < / s p an >< s p an c l a ss = " m c l ose " >< s p an c l a ss = " m c l ose " > ) < / s p an >< s p an c l a ss = " m s u p s u b " >< s p an c l a ss = " v l i s t − t " >< s p an c l a ss = " v l i s t − r " >< s p an c l a ss = " v l i s t " s t y l e = " h e i g h t : 0.8141 e m ; " >< s p an s t y l e = " t o p : − 3.063 e m ; ma r g in − r i g h t : 0.05 e m ; " >< s p an c l a ss = " p s t r u t " s t y l e = " h e i g h t : 2.7 e m ; " >< / s p an >< s p an c l a ss = " s i z in g rese t − s i ze 6 s i ze 3 m t i g h t " >< s p an c l a ss = " m or d m t i g h t " > 3 < / s p an >< / s p an >< / s p an >< / s p an >< / s p an >< / s p an >< / s p an >< / s p an >< / s p an >< / s p an >< / s p an >< / s p an > . < ! − − L A TE X P ROCESSE D 1 756993854718 − − >< / s t ro n g >< / p >< p >< e m > A ˊ p d ụ n g c o ^ n g t h ứ c :< / e m >< / p >< d i v c l a ss = " ma t h − b l oc km y − 4 t e x t − ce n t er " >< d i v c l a ss = " ma t h − d i s pl a y " ro l e = " im g " a r ia − l ab e l = " M a t h e ma t i c a l e x p ress i o n : $ - Cách ghi nhớ hiệu quả: Hãy nhớ đúng thứ tự dấu “+, -, +, -” và lưu ý hệ số 1-3-3-1 kèm theo lũy thừa giảm dần củaa a a b b b
- Điều kiện sử dụng: Chỉ sử dụng khi hiệu ở cùng dạng( a − b ) 3 (a-b)^3 ( a − b ) 3
- Biến thể: Dạng tổng quát hơn là lập phương của một tổng( a + b ) 3 = a 3 + 3 a 2 b + 3 a b 2 + b 3 (a+b)^3 = a^3 + 3a^2b + 3ab^2 + b^3 ( a + b ) 3 = a 3 + 3 a 2 b + 3 a b 2 + b 3
3. Ví dụ minh họa chi tiết 3.1 Ví dụ cơ bản Ví dụ: Tính( 2 − 1 ) 3 (2-1)^3 ( 2 − 1 ) 3
Giải từng bước:
Áp dụng công thức:( a − b ) 3 = a 3 − 3 a 2 b + 3 a b 2 − b 3 (a-b)^3 = a^3 - 3a^2b + 3ab^2 - b^3 ( a − b ) 3 = a 3 − 3 a 2 b + 3 a b 2 − b 3 a = 2 a=2 a = 2 b = 1 b=1 b = 1 2 3 − 3 i m e s 2 2 i m e s 1 + 3 i m e s 2 i m e s 1 2 − 1 3 = 8 − 12 + 6 − 1 = 1 2^3 - 3imes2^2imes1 + 3imes2imes1^2 - 1^3 = 8 - 12 + 6 - 1 = 1 2 3 − 3 im es 2 2 im es 1 + 3 im es 2 im es 1 2 − 1 3 = 8 − 12 + 6 − 1 = 1 Lưu ý: Cẩn thận khi thay số, đừng quên dấu trừ!
3.2 Ví dụ nâng cao Ví dụ: Rút gọn biểu thức( x − 2 y ) 3 (x-2y)^3 ( x − 2 y ) 3
Áp dụng công thức:
' in math mode at position 1:
$' in math mode at position 1:$
̲(x-2y)^3 = x^3 …" style="color:#cc0000">$(x-2y)^3 = x^3 - 3x^2 extcolor{red}{(2y)} + 3x extcolor{red}{(2y)^2} - (2y)^3
$$$(x-2y)^3 = x^3 - 3x^2 extcolor{red}{(2y)} + 3x extcolor{red}{(2y)^2} - (2y)^3$$
$
Biểu đồ cột thể hiện giá trị của từng hạng tử trong khai triển (a-b)^3 với a=2, b=1: a^3 = 8, -3a^2b = -12, 3ab^2 = 6, -b^3 = -1 và tổng các hạng tử = 1
Tính các hạng tử:
x 3 x^3 x 3 − 3 x 2 i m e s 2 y = − 6 x 2 y -3x^2imes2y = -6x^2y − 3 x 2 im es 2 y = − 6 x 2 y 3 x i m e s ( 2 y ) 2 = 3 x i m e s 4 y 2 = 12 x y 2 3ximes(2y)^2 = 3ximes4y^2 = 12xy^2 3 x im es ( 2 y ) 2 = 3 x im es 4 y 2 = 12 x y 2 − ( 2 y ) 3 = − 8 y 3 -(2y)^3 = -8y^3 − ( 2 y ) 3 = − 8 y 3
⇒ ( x − 2 y ) 3 = x 3 − 6 x 2 y + 12 x y 2 − 8 y 3 \Rightarrow (x-2y)^3 = x^3 - 6x^2y + 12xy^2 - 8y^3 ⇒ ( x − 2 y ) 3 = x 3 − 6 x 2 y + 12 x y 2 − 8 y 3 $$\Rightarrow (x-2y)^3 = x^3 - 6x^2y + 12xy^2 - 8y^3$$
Kỹ thuật giải nhanh: Nhận diện các dạng( a − b ) 3 (a-b)^3 ( a − b ) 3
4. Các trường hợp đặc biệt - Nếua = b a = b a = b ( a − b ) 3 = 0 (a-b)^3 = 0 ( a − b ) 3 = 0 b = 0 b = 0 b = 0 ( a − 0 ) 3 = a 3 (a-0)^3 = a^3 ( a − 0 ) 3 = a 3 a a a
5. Lỗi thường gặp và cách tránh 5.1 Lỗi về khái niệm - Hiểu nhầm giữa lập phương của hiệu và hiệu của lập phương:( a − b ) 3 ≠ a 3 − b 3 (a-b)^3 \neq a^3 - b^3 ( a − b ) 3 = a 3 − b 3 ( a − b ) 3 (a-b)^3 ( a − b ) 3 a 3 − b 3 a^3 - b^3 a 3 − b 3
5.2 Lỗi về tính toán - Nhầm dấu các hạng tử (cộng, trừ sai dấu).a = 2 ; b = 1 a=2; b=1 a = 2 ; b = 1
6. Luyện tập miễn phí ngay Truy cập kho 42.226+ bài tập "Tính lập phương của một hiệu" miễn phí, luyện tập không cần đăng ký, bắt đầu học ngay, theo dõi tiến độ và cải thiện kỹ năng từng ngày. Đừng bỏ lỡ cơ hội luyện tập Tính lập phương của một hiệu miễn phí để nắm vững dạng bài này!
7. Tóm tắt và ghi nhớ Nhớ công thức( a − b ) 3 = a 3 − 3 a 2 b + 3 a b 2 − b 3 (a-b)^3 = a^3 - 3a^2b + 3ab^2 - b^3 ( a − b ) 3 = a 3 − 3 a 2 b + 3 a b 2 − b 3 Phân biệt với hiệu của lập phươnga 3 − b 3 a^3-b^3 a 3 − b 3 Đọc kỹ đề, kiểm tra kỹ dấu từng hạng tử. Luyện nhiều dạng bài, tự kiểm tra bằng thay số cụ thể. Lập dàn ý ôn tập: Định nghĩa – Công thức – Ví dụ – Lỗi sai – Luyện tập. 
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