2cos^2 x/4-2sin^2 x/4=-1 решить уравнение

2cos^2 x/4 -2sin^2x/4= -1, 2(cos^2 x/4 - sin^2 x/4)= -1, (cos^2 x/4 - sin^2 x/4) = -1/2, cos(2(x/4))= -1/2, cos(x/2)= -1/2, x/2=+-2π/3+2πk, k∈Z,  x=+-4π/3 +4πk, k∈Z