\(\left|x\left(x-4\right)\right|=x\)
\(\Rightarrow\left[{}\begin{matrix}-x\left(x-4\right)=x\\x\left(x-4\right)=x\end{matrix}\right.\Rightarrow\left[{}\begin{matrix}x-4=-1\\x-4=1\end{matrix}\right.\)
\(\Rightarrow\left[{}\begin{matrix}x=3\\x=5\end{matrix}\right.\)