Hằng đẳng thức dạng ( A – B ) ( A^2 + AB + B^2) = A^3 – B^3
a) ( 3x – 1 ) ( 9x^2 + 3x +1 )
b) ( 1/2 -x ) ( 1/4 + 1/2 x + x^2 )
Hằng đẳng thức dạng ( A – B ) ( A^2 + AB + B^2) = A^3 – B^3 a) ( 3x – 1 ) ( 9x^2 + 3x +1 ) b) ( 1/2 -x ) ( 1/4 + 1/2 x + x^2 )
By Nevaeh
`a)(3x-1).(9x^2+3x+1).`
`=(3x-1).[(3x)^2+3x.1+1^2].`
`=(3x)^3-1^3.`
`b) (1/2-x).(1/4+1/2x+x^2).`
`=(1/2-x).[(1/2)^2+1/2.x+x^2].`
`=(1/2)^3-x^3.`
a) `(3x-1)(9x^2+3x+1)=(3x-1)[(3x)^2+3x.1+1^2]=3x^3-1^3`
b) $\bigg(\dfrac{1}{2}-x\bigg)\bigg(\dfrac{1}{4}+\dfrac{1}{2}x+x^2\bigg)=\bigg(\dfrac{1}{2}-x\bigg)\Bigg[\bigg(\dfrac{1}{2}\bigg)^2+\dfrac{1}{2}x+x^2\Bigg]=\bigg(\dfrac{1}{2}\bigg)^3-x^3$