Решите уравнение sin^4x-cos^4x+2cos^2x=cos2x

(sin^2x + cos^2x) (sin^2x - cos^2x) = cos2x - 2cos^2x

sin^2x - cos^2x = cos^2x - sin^2x - 2cos^2x = - 1

1 - cos^2x - cos^2x = - 1 - > cos^2x = 1 - >

cosx = 1 или cosx = - 1 - > x = πn n ∈ Z