Could someone please give me the proofs, or point me to a website, of the compound angles formulae?

That is:

cos(A+B) = cosA.cosB - sinA.sinB

And the other ones, cos(A-B), sin(A+B), sin(A-B), tan(A+B), tan(A-B).

Are they just geometrical proofs, or are there algebraic ones? Thank-you.