Hey,

I'm doing a problem in which we are supposed to solve for cos7.5 degrees using the half-angle identities.

I got to +/- square root of (1+cos15)/2, and can't figure out how to find cos15(without just putting it into a calculator) so that I can solve the problem. Did I set this up correctly? If so, then how do I find the cosine of this angle? Thanks!