1+cosx= ctg x/2 надо решить с половинного угла

1+cosx= ctg x/2 
1 + 2cos^2(x/2) = ctg(x/2)
2cos^2(x/2) = (cos(x/2)) / (sin(x/2)
2cos(x/2)*sin(x/2) = 1
sinx = 1/2
x = (-1)^n*arcsin(1/2) + πn, n∈z
x = (-1)^n*(π/6) + πn, n∈z