The task is to prove that they are equal ;)

I think what you mean is this:



This comes directly from substituting the identities:



You will also use:

Post back to show us your progress, and if you're still stuck we can help you along.

h,I at first thank you very much for trying to help me ;) but the first part it should be 45 degrees and than the last member should be 1/2- sin2x (not squared) and I need to prove that they are equal so I need the whole modifying procedure