prove the identity: cos^4 - sin^4 = cos^2 - sin^2
(cos^2 + sin^2)(cos^2 - sin^2)
cos^2 + sin^2 = 1
cos^2 - sin^2 = cos^2 - sin^2
is this correct?
(cos^2 + sin^2)(cos^2 - sin^2)
cos^2 + sin^2 = 1
cos^2 - sin^2 = cos^2 - sin^2
is this correct?