Cos^2x-sin^2x/sin^4x-cos^4x
Simplify
sin^2 + cos^2 = 1
(sin^2 + cos^2)(sin^2 - cos^2) = sin^4 - cos^4
cos^2 - sin^2 = -(sin^2 - cos^2)
simplifies to -1
Simplify
(sin^2 + cos^2)(sin^2 - cos^2) = sin^4 - cos^4
cos^2 - sin^2 = -(sin^2 - cos^2)
simplifies to -1