(A) sin(-x) = -sinx
(B) cos(-x) = cosx
(C) cos(x+y) = cosx cosy + sinx siny
(D) sin(x+y) = sinx cosy + cosx siny
I'm stuck on the very first question:
(a) sin²x + cos²x = 1 (use (C) and cos0 = 1)
the answers also say to use (A) and (B).. but I dunno how that would apply. It also said to use x = y. How am I supposed to use cos0 though?
thanks in advance for the help!