1. The problem statement, all variables and given/known data Prove the identity: Cosh(x) + Cosh(y) = 2Cosh[(x+y)/2]Cosh[(x-y)/2] 2. Relevant equations Cosine sum-to-product http://library.thinkquest.org/17119/media/3_507.gif 3. The attempt at a solution Can you use the same formula for Cosine sum to product for hyperbolic cosine? Thanks!