Proving trig identities
I have 2 more this time, thanks for the time!
Homework Statement
-sin^2x-sin^2y+1=cos(x+y)cos(x-y)
Homework Equations
Compound, double, pythagorean, reciprocal, quaotient, etc.
The Attempt at a Solution
R.H.S.
cos(x+y)cos(x-y)
=...