3 sin²x+10sin x cos x+3cos² x =0 | : cos² x
3tg² x+10tg x+3=0
D=100-36=64
tg x= (-10+8)/6= -1/3 tg x= -1/3 x= - arctg(1/3)+πn n∈Z
tg x=(-10-8)/6 = -3 tg x= -3 x= - arctg (3)+πn n∈Z
