сos²x-sin²x=cos2x
cos2x=√2
2x=±arccos√2+2πn
x=±0,5 *arccos√2+πn , n∈Z
(1-sin^2(x))-sin^2(x)=sqrt(2)
1-2sin^2(x)=sqrt(2)
-2sin^2(x)=sqrt(2)-1
sin^2(x)=(sqrt(2)-1)/2
sinx=sqrt((sqrt(2)-1)/2)
x=(-1)^k*arcsin (sqrt((sqrt(2)-1)/2)) + p*k, k=Z
