Identities BOB

In this unit I pretty much understood everything. The part where Mr. K was proving how the whole sine dance equations worked kind of threw me off at first. My muddiest point is proving that one side is identical to the other. I just don't know where to start sometimes. Do I change everything to sine and cosine? Do I use the Pythagorean identity to make substitutions? Do I factor? Do I multiply by 1? I guess I just have to practice a little more. Another thing is some of the questions that were on the pre-test (number 2 and 3) where you had to find the cos(a-b) and it gives you two angles, questions like that. That's... pretty much it.