Let's verify the identity

How can we simplify the right-hand side?

** A. ** ** B. ** ** C. ** ** D. ** ** E. ** ** F. ** ** G. ** None of the above

How can we finish the proof?

** A. ** The previous equation is just the double angle formula for sine.** B. ** The previous equation is just the double angle formula for cosine.** C. ** Multiply by ** D. ** Apply the Pythagorean Identity to get that the left and right hand sides are equal.** E. ** None of the above