\(f(x) = \left\{\begin{array}2x − 5 & x\geq 3\\1 & 2 < x < 3\\−2x +5 & x\geq 2\end{array}\right.\)

\(f^⁄(x) = \left\{\begin{array}22 & x\geq 3\\0 & 2 < x < 3\\−2 & x\geq 2\end{array}\right.\)

 \(f^⁄(x)\) changes as value of x changes.

Hence function is not differentiable as left side and right side of  \(f^⁄(x)\) at \(x=3\) is different.