im trying to remember how to do some trig. first of all, how do you find cos^-1 (5/3) without using a calculator? 2nd, i need help proving this identity: 2sin^2(x) - cos (x) - 2 sin (x) + 1 = 0 3rd, how do you evaluate sin 165 (which is sin (11/12 pi)) again without using a calculator. thanks for the help. i know im suppose to try them first but i havent done this in a while and im really stuck. also if someone could give me a good trig link so i can refresh on my trig, id appreciate it.