2cos^2(3x)-cos(3x)=0 решить надо

2cos^2(3x) - cos(3x) = 0
cos(3x)*(2cos3x - 1) = 0
1)  cos3x = 0
3x = π/2 + πn, n∈Z
x1 = π/6 + πn/3, n∈Z
2)  2cos3x - 1 = 0
cos3x = 1/2
3x = (+ -)*arccos(1/2) + 2πk,k∈Z
3x = (+ -)*(π/3) + 2πk,k∈Z
x2 = (+ -)*(π/9) + 2πk/3, k∈Z