Question

Identify the open intervals on which the function is increasing or decreasing.
f(x) = 9 cos^2 x − 9 cos x, 0 < x < 2π

Answer 1

find f'(x) and check the intervals when f'(x) is positive and negetive.
f'(x)>0, f is increasing.
f'(x)<0, f is decreasing.

Answer 2

yea i know the process but this problem throws me off

Answer 3

do you need the steps?