(A) $\sin(-x)=-\sin x$
(B) $\cos(-x)=\cos x$
(C) $\cos(x+y)=\cos x\cos y-\sin x\sin y$
(D) $\sin(x+y)=\sin x\cos y+\cos x\sin y$
Use these equalities to derive the following important trigonometric functions:
(b) $\sin 2x=2\sin(x)\cos(x)$
I know I've asked this same question about a month ago, but I just got back to this problem in my packet and I have yet to come up with anything. For (a), I may have gotten it. So please check here. I moved on to the second one and I have no idea how to start this one off. It's just a confusing question I think. Can someone at least tell me which equation(s) to use and why? Thanks a lot.