Tìm x biết a,(x-2).(x^2+2x+7) + 2 (x^2-4) – 5(x-2)=0 b, x^3+27+(x+3)(x-9)=0

`a,(x-2)(x^2+2x+7)+2(x^2-4)-5(x-2)=0`

$\Leftrightarrow\left(x-2\right)\left(x^2+2x+7+2x+4-5\right)=0$

$\Leftrightarrow\left(x-2\right)\left(x^2+4x+6\right)=0$

`⇔x-2=0`

$\Leftrightarrow x=2$

`b, x^3+27+(x+3)(x-9)=0`

$⇔x^3+3^3+\left(x+3\right)\left(x-9\right)=0$

$⇔\left(x+3\right)\left(x^2-3x+9\right)+\left(x+3\right)\left(x-9\right)=0$

$⇔\left(x+3\right)\left(x^2-3x+9+x-9\right)=0$

$⇔x\cdot\left(x+3\right)\cdot\left(x-2\right)=0$

$\Rightarrow\left\{{}\begin{matrix}x=0\\x+3=0\\x-2=0\end{matrix}\right.$

$\Rightarrow\left\{{}\begin{matrix}x=0\\x=-3\\x=2\end{matrix}\right.$

Xin hay nhất !