\(x\left(x+4\right)=0\)
\(\Rightarrow\left[{}\begin{matrix}x=0\\x+4=0\end{matrix}\right.\)
\(\Rightarrow\left[{}\begin{matrix}x=0\\x=0-4\end{matrix}\right.\)
\(\Rightarrow\left[{}\begin{matrix}x=0\\x=-4\end{matrix}\right.\)
Vậy \(x\in\left\{0;-4\right\}\)
