f(x) = 3cos(x)−cos^3(x) for 0 < x < 2π

Question

I need help finding where it increases and decreases and where it concaves up and down.

The inflection points I have found are pi/2 and 3pi/2.

Answer 1

f(x) increases where f'(x) > 0.
f(x) is concave up when f"(x) > 0.