Okay these are giving me such a problem to figure out. I have to use these 4 identities to prove others.

A. sin(-x) = - sinx

B. cos(-x) = -cosx

C. cos(x+y) = cosxcosy-sinxsiny

D. sin(x+y) = sinxcosy + cosxsiny

these are what i have to derive.

cos2x=1-2sin^2x

Abslout value of cos(x/2) = Squareroot of ((1+cosx)/2)

Abslout value of sin(x/2) = Squareroot of ((1-cosx)/2)

Any help is much apprecieted. Thanks alot!