f'(x)=\left\{
\begin{array}{ll}
(x^3-2x(x-2))', & x>2\vspace{0.5em}\\
(x^3-2x(2-x))', & x<2
\end{array}
\right.
=
\left\{
\begin{array}{ll}
3x^2-4x+2, & x>2\vspace{0.5em}\\
3x^2+4x-2, & x<2
\end{array}
\right.