The function f is differentiable on a closed interval [-6, 5]. The graph of f, the derivative of f, consists of 3 line segments and a semicircle as shown. (-6, 2) (3, 2) a) On what intervals is f increasing? Justify your answer. O (-6,-2)U(2,5) Graph of f' b) On what intervals is f concave down? Justify your answer. c) For f'(-5) and f'(3), find the value or explain why it does not exist