Easy# Find All Points of Non-differentiability, Horizontal Tangents

APCALC-VGJCOQ

The graph of the function $f$ shown in the figure below has a vertical tangent at the point $(2,0)$ and horizontal tangents at the points $(0,2)$ and $(4,-2)$.

For what values of $x, \hspace{.2cm} -6 \lt x \lt 6$, is $f$ not differentiable?