\(a, x^3-2x^2-x+2=0\)
\(\Leftrightarrow\left(x^3-x\right)-\left(2x^2-2\right)=0\)
\(\Leftrightarrow x\left(x^2-1\right)-2\left(x^2-1\right)=0\)
\(\Leftrightarrow\left(x^2-1\right)\left(x-2\right)=0\)
\(\Leftrightarrow\left[{}\begin{matrix}x^2-1=0\\x-2=0\end{matrix}\right.\)
\(\Leftrightarrow\left[{}\begin{matrix}x=\pm1\\x=2\end{matrix}\right.\)