cos 3x = - 1/2 решите уравнение

cos3x = -¹/₂3x = ± (π - arccos¹/₂) + 2πn, n ∈ Z3x = ± (π - π/3) + 2πn, n ∈ Z3x = ± 2π/3 + 2πn, n ∈ Zx = ± 2π/9 + 2πn/3, n ∈ Z