I know it sounds like a stupid question. Mixing trig into calc usually breaks my algebraic intuitions.
I just don't get how cos (x) and sin(x) get factored out in the last step. I tried watching videos from MIT OCW and youtube where the proof is demonstrated, but they always just write it out...
I understand everything in the proof except the last step I have written here. What comes after, I understand.
How is it that the cosine and sine are able to be factored out of the fraction? That one step gets me. I was never too good with my trig, and have finally gotten a decent grasp of...