Let $f(x)=(x-2)^{2 / 3}$.
a. Does $f^{\prime}(2)$ exist?
b. Show that the only local extreme value of $f$ occurs at $x=2$.
c. Does the result in part (b) contradict the Extreme Value Theorem?
d. Repeat parts (a) and (b) for $f(x)=(x-a)^{2 / 3}$, replacing 2 by $a$.