sin²x + cos²x =1
cos²x = 1 - sin²x
3 cos²x = 3(1 - sin²x)
2sin² x + 3cos²x + 2sin x = 0
2sin²x + 1 - sin²x + 2 sin x = 0
1 + 2 sin x =0
2 sin x = -1
sin x = -0,5
x = -π/6
x[1]=11π/6 + 2kπ
x[2]=7π/6 + 2kπ
