sin^4x/2-cos^4x/2=1/2
(sin^2x/2-cos^2x/2)*(sin^2x/2+cos^2x/2)=1/2
sin^2x/2-cos^2x/2 = 1/2
cos x = - 1/2
x=пи-пи/3+2пи*nх=±2пи/3+2пи*n
