3)sin^2x+3cosx+17=0
1-cos^2x+3cosx+17=0
cos^2-3cosx+18=0
cosx=y
y^2-3y+18=0
D=81
x1=6
x2=-3
1)cosx=6
x=+-arccos6+2Пn
2)cosx=-3
x=+-arccos(-3)+2Пn
3)sin^2x+3cosx+17=0
1-cos^2x+3cosx+17=0
cos^2-3cosx+18=0
cosx=y
y^2-3y+18=0
D=81
x1=6
x2=-3
1)cosx=6
x=+-arccos6+2Пn
2)cosx=-3
x=+-arccos(-3)+2Пn