Sin (p/3-2x)=-1/2 [0;90] градусов

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

А синус с косинусом не перепутали? О.о