Suppose a function f is differentiable on (−3,2) and its derivative satisfies
f′(x)>0 for −3<x<0, f′(0)=0, and f′(x)<0 for 0<x<2.
a) On which sub-interval of (−3,2) is f strictly increasing?
b) On which sub-interval of (−3,2) is f strictly decreasing?