Question

Verify The Identity. cos (x - y) - cos (x + y) = 2 sin x sin y

Answer 1

Do you know the double formulae for cos?

Answer 2

No I have been absent for 3 days and missed how to do this.

Answer 3

This might help_

cos (x - y) = cos x cos y + sin x sin y
cos (x + y) = cos x cos y - sin x sin y