Hey there, I'm not sure where the majority of this community reside, but I'm David and I live in England. I study Maths at A2 Level, (C3). I'm not sure if that's what it's called overseas but I hope it's the same or there's an equivalent.

Anyway, I'm having problems with double and half angle formula application and useage. I've been given a question, and I'd be so undoubtedly greatful if one of you mighty maths minds could work it through for me. Here it is:

Using the identity for cos (A+B), prove that cos θ = 1 - 2 sin² (½θ).

Probably looking at this, you're thinking I'm a complete amateur, but I don't have a clue; I'm stumped. Please help!

Cheers, David.