Answer:
D sqrt 1+cos(x)
Explanation:
You have to multiply both the top and the bottom by the same thing, because you are essentially multiplying the equation by 1 here, and any number over itself is equivalent to 1 over 1. The reason for this is because you are proving the identity, which means that you can only multiply by 1 or things that equal 1, because you are trying to PROVE that one side equals the other, so you can't rely on the normal processes that you would use to solve a system of equations.