Prove that:

Question

2sinxsiny = cos(x-y) - cos(x+y)

Answer 1

Rewrite the right side, using
cos (x + y) = cos x cos y - sin x sin y
cos (x - y) = cos x cos y + sin x sin y
You should be familiar with those two identities.

Answer 2

kagr

Answer 3

To price this equation first subtract cos(x-y) and cos(x+y)
=cosXcosY + sinXsinY
-(cosXcosY-sinXsinY)
= 2sinXsinY
Hence , proved!