Recent content by HHermans

Thanks very much for everyone's help, I now understand this. cos(x + y) can be written as cos(x + -x), or cos(0).

I've tried this a few times, and I got nowhere. Is there a specific direction to go?

For a homework assignment I'm supposed to prove that sin(x)^2+cos(x)^2=1, using only the following identities (along with algebraic operations): sin(-x)=-sin(x) cos(-x)=cos(x) cos(x+y)=cos(x)cos(y)-sin(x)sin(y) sin(x+y)=sin(x)cos(y)+cos(x)sin(y) I can't figure this out, because as far...