Question

Prove that: (cosx + cosy)^2 + (sinx - siny)^2 = 4 cos^2 (x+y)/2?

Answer 1

cos^2 x + cos^2 y + 2cox cos y + sin^2 x + sin^2 y - 2 sinx siny

Answer 2

2 ( 1 + cos(x + y)} and i am stuck here