My problem is:
Establish the identity.
cos (α + β) + cos (α - β) = 2 cos α cos β
Any help would be greatly appreciated. Thanks!
Leave the right side alone. Take the left side and evaluate it using the sum/difference formula and I'll bet you will end up with what is on the right side. All the question is asking you to do is establish the identity or prove that what is one the left is equal to what is on the right. You can do that by just evaluating the left side.