cosx - cosy=-2 sin(x + y/2) sin(x - y/2)
dont know what identities to use
The Attempt at a Solution
ok so when i figure it out, the RHS always comes out to either...
(cos x sin y - sin x cos y)/2
cos x sin y - sin x cos y without the divided by 2 part
it never equals the LHS=cosx - cosy