7sin^2(5π+x)-cos(3π/2+x)*cos(x-7π)=6

Question

7sin^2(5π+x)-cos(3π/2+x)*cos(x-7π)=6

Answer 1

7sin^2x-sinx*cosx-6=0

7tg^2x-tg-6=0

tgx=t

7t^2-t-6=0

D=169

x1,2=1-+13/14=  x1=-6/7; x2=1

tgx=1

x=pi/4+pik

 

x=arctg(-6/7)+pik

 

Вроде так