Question

Integration of cos2x-cos2y ÷cosx-cosy

Answer 1

(cos2x-cos2y)/(cosx-cosy)

=2sin(x+y)sin(y-x)/2sin(x+y)/2.sin(y-x)/2

={4sin(x+y)/2.cos(x+y)/2.sin(y-x)/2.cos(y-x)/2}/sin(x+y)/2.cos(y-x)/2

=4cos(x+y)/2.cos(y-x)/2