1) cosx<-½

2) sin>½

3) 6sin²x-4sin²x-1

6sin ^ 2x-4sin2x + 1 = 0

6sin ^ 2x-8sinxcosx + (sin^2x+cos^2x) = 0

7sin ^ 2x-8sinxcosx + соs^2x = 0 - delim na cos^2x

7tg^2x-8tgx+1=0

Замена: tgx=a

7a^2-8a+1=0

a1=1; a2=1/7

Reshaem 2 uravneniya:

1) tgx=1

x=arctg1+Pin=Pi/4+Pin;

2) tgx=1/7

x=arctg1/7+Pin; (n принадлежит Z)