I am having trouble determining the extrema of the above function. I think the derivative is 2 cos x - 2 sin 2x At 2 cos x= 0 ; cos is pi/2 and/or 3 pi/2. At - 2 sin 2x = 0; - 2 sin 2x = pi and/or 2 pi. 2 cos x = pi, ---> cos x = pi/2 and/or 3 pi/4. - 2 sin 2x = -pi/2 ---> - pi/4 or - pi/2. If what I did so far is correct, I do not understand how to use the information to determine the extrema of x a 0 less than or equal than x less than or equal than 2 pi.