\(x^3-x=0\Leftrightarrow x\left(x^2-1\right)=0\Leftrightarrow\left(x-1\right)x\left(x+1\right)=0\Leftrightarrow\left[{}\begin{matrix}x-1=0\\x=0\\x+1=0\end{matrix}\right.\Leftrightarrow\left[{}\begin{matrix}x=1\\x=0\\x=-1\end{matrix}\right..Vậy:x\in\left\{-1;0;-1\right\}\)
\(x^3+4x=0\Leftrightarrow x\left(x^2+4\right)=0\Leftrightarrow\left[{}\begin{matrix}x=0\\x^2+4=0\end{matrix}\right.mà:x^2+4\ge0+4=4\Rightarrow x=0\)
\(\left(x+2\right)^2=x+2\Leftrightarrow\left(x+2\right)\left(x+2-1\right)=0\Leftrightarrow\left(x+1\right)\left(x+2\right)=0\Leftrightarrow\left[{}\begin{matrix}x+1=0\\x+2=0\end{matrix}\right.\Leftrightarrow\left[{}\begin{matrix}x=-1\\x=-2\end{matrix}\right.\)
