i know they are difference of squares but i dont know what to do after....the answer is -root3over2
We are given to evaluate:
You are right, recognizing this as a difference of squares is a good start:
Next, with the angle sum/difference identities for cosine in mind, let's rewrite this as:
The first factor should look familiar as a Pythagorean identity, and the second factor should look familiar as a double-angle identity for cosine...