Cos^2x-sin^2x/sin^4x-cos^4x

Question

Simplify

Answer 1

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