3sin2 x + 10sin x cos x + 3cos2 x = 0
sin(2x)=x(-3sin(2)/5-3cos(2)/5)
3x sin(2)+5sin(2x)+3x cos(2)=0
5 sin(2x)+3x (sin(2)+cos(2))=0
x=-2,68301
x=-1,86266
x=0
x=1,86266
x=2,68301
