f '(−2) = 0
Translation: the slope of f(x) is zero at x = −2. Note: x = −2 is a CANDIDATE for local max or min. (It might also be a point of inflection.)
f '(3) = DNE
Reasons why a derivative might not exist at a point:
f ''(x) < 0 for x < 3 and f ''(x) > 0 for x > 3
Translation: There is a change in concavity at x = 3.