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vectors a and b exist in the x,y plane and make angles (alpha) and (beta) with x.

(Ill use A as alpha and B as beta)

prove: cos (A-B) = cos(A)cos(B)+sin(A)sin(B)

prove: sin (A-B) = sin(A)cos(B) - cos(A)sin(B)

I think there is some relationship (for the first one) to this:

r.s= rscos(theta), but I really don't know where to start with this one..