помогите решить неравенство) sin 2x*sin x - cos2x*cosx

sin(2x)*sin(x) - cos(2x)*cos(x) ≤ 1/2

2sin(x)cos(x) - (1 - 2sin(x))*cos(x) ≤ 1/2

2sin(x)cos(x) - cos(x) + 2sin(x)cos(x) ≤ 1/2

4sin(x)cos(x) - cos(x) ≤ 1/2

cos(x)*(4sin(x) - 1) ≤ 1/2

cos(x)*(4 - 4cos(x) - 1) ≤ 1/2

cos(x)*(-4cos(x) +3) ≤ 1/2

-4cos(x) + 3cos(x) ≤ 1/2

-cos(3x) ≤ 1/2

cos(3x) ≥ -1/2

x ∈ [-2π/9 + 2πk/3; 2π/9 +2πk/3], k - целое

Ответ: [-2π/9 + 2πk/3; 2π/9 +2πk/3]