The function f(x) = sin (x + sin 2x), 0 < x < , arises in applications

Question:

The function f(x) = sin (x + sin 2x), 0 < x < π, arises in applications to frequency modulation (FM) synthesis.
(a) Use a graph of f produced by a graphing device to make a rough sketch of the graph of f’.
(b) Calculate f’(x) and use this expression, with a graphing device, to graph .
Compare with your sketch in part (a).