Sin (p/3-2x)=-1/2 [0;90] градусов

А синус с косинусом не перепутали? О.о

cos(π/6+2x)=-1/2π/6+2x=-π/3+2πn.n∈z U π/6+2x=π/3+2πk,k∈z2x=-π/2+2πn,n∈z U 2x=π/6+2πk,k∈zx=-π/4+2πn,n∈z U x=π/12+2πk,k∈xx=π/12∈[0;π/2]