Question: Determine all values of x, $-10<x<10$ such that the indicated function is not differentiable

(a) $f\left( x \right)=x|x|$

(b) $f\left( x \right)=|{{x}^{2}}-1|$

(c) $f\left( x \right)={{\left( 1-{{x}^{2/3}} \right)}^{3/2}}$