Cos(6x)+6cos^2(3x)=1

cos6x + 6cos²3x = 1 cos²3x - sin²3x + 6cos²3x = 1 7cos²3x - sin²3x = 1 7cos²3x - (1 - cos²3x) = 1 7cos²3x - 1 + cos²3x = 1 8cos²3x = 2 4cos²3x = 1 cos²3x = 1/4 cos3x = 1/2 cos3x = -1/2 3x = -π/3 + 2πn 3x = π/3 + 2πn 3x = 2π/3 + 2πn 3x = -2π/3 + 2πn x = -π/9 + 2πn/3 x = π/9 + 2πn/3 x = 2π/9 + 2πn/3 x = -2π/9 + 2πn/3 OTBET: -π/9 + 2πn/3; π/9 + 2πn/3; -2π/9 + 2πn/3; 2π/9 + 2πn/3; n ∈ Z