tìm x biết x^3 - 4x = 0

* Hướng dẫn giải

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