2Cos²x - 3Sinx = 0
Cos²x + Sin² = 1 => Cos²x = 1 - Sin²x
2(1 - Sin²x) - 3Sinx = 0
2 - 2Sin²x - 3Sinx = 0
-2Sin²x - 3Sinx + 2 = 0
2Sin²x + 3Sinx - 2 = 0
Sinx = t ∈ [-1;1]
2t² + 3t - 2 = 0
D = 9 - 4 * 2 * (-2) = 25
t₁ = (-3 + √25) / 4 = 1/2
t₂ = (-3 - √25) / 4 = -2 ∉ [-1;1]
Sinx = 1/2
x = π/6 + 2πn, n∈Z
x = 5π/6 + 2πn, n∈Z