we have

use the formulas

and

to keep breaking down the sines and cosines until you get them to and . then use the double angle formulas. then simplify and continue. it will be a lot of work, but it is the kind of work where you can keep following your nose

use the double angle formulas for sine15. sin2x = cosx

(on the interval [0, 2pi])

now continue

EDIT: This is my 53th post!!!!!!!