5sin(x/6)-(1-2sin^2(x/6))+3=0
5sin(x/6)-1+2sin^2(x/6)+3=0
2sin^2(x/6)+5sin(x/6)+2=0
пусть sin(x/6)=t
2t^2+5t+2=0
D=25-16=9=3^2
t1=-1/2 t2=-2
sin(x/6)=-1/2 sin(x/6)=-2
не существует, т.к. -1≤sinx≤1
x/6=arcsin(-1/2)+2πn
x/6=π-arcsin(-1/2)+2πn
x/6=-π/6+2πn
x/6=7π/6+2πn
x1=-π+12πn
x2=7π+12πn