Tìm x, biết x^2 (x+3) - 4x -12 = 0

* Hướng dẫn giải

$\begin{array}{l}{\mathrm{x}}^2\left(\mathrm{x}+3\right)-4\mathrm{x}-12=0\\ {\mathrm{x}}^2\left(\mathrm{x}+3\right)-4\left(\mathrm{x}+3\right)=0\\ \left(\mathrm{x}+3\right)\left({\mathrm{x}}^2-4\right)=0\\ \left(\mathrm{x}+3\right)\left(\mathrm{x}+2\right)\left(\mathrm{x}-2\right)=0\Rightarrow \left[\begin{array}{l}\mathrm{x}=-3\\ \mathrm{x}=-2\\ \mathrm{x}=2\end{array}\right.\end{array}$