Prove that the left equals the right
So far I've multiplied to get a common denominator of And have the numerator of Past this I can't think of where to go.
I will use s & c for sine and cosine respectively.
First convert the LHS to sines and cosines:
Now simplify a bit:
Put everything into one fraction and use the sum of cubes factorization:
The (s+c) terms cancel leaving
And now you are one identity from completing the problem.