rút gọn ( x- 3) (x^2 +3x +9)-(x^2 +3)(x- 9) tìm x (2x-3 ) (3+2x) -x (x-1 ) =3(x-1)^2

Đáp án:

`( x- 3) (x^2 +3x +9)-(x^2 +3)(x- 9)`

`=x^3-27-[x^3-9x^2+3x-27)`

`=x^3-27-x^3+9x^2-3x+27`

`=9x^2-3x`

`=3x(3x-1)`

tìm `x`

`(2x-3 )(3+2x)-x(x-1 )=3(x-1)^2`

`<=>(2x-3 )(3+2x)-x(x-1 )-3(x-1)^2=0`

`<=>4x^2-9-x^2+x-3(x^2-2x+1)=0`

`<=>4x^2-9-x^2+x-3x^2+6x-3=0`

`<=>-12+7x=0`

`<=>7x=0+12`

`<=>7x=12`

`<=>x=12/7`