6sin^2(x)+5cos(x)-7=0
6*(1-cos^2(x))+5cos(x)-7=0
6-6cos^2(x)+5cos(x)-7=0
6cos^2(x)-5cos(x)+1=0
cos(x)=t
6t^2-5t+1=0
D=1
t1=0,5
t2=1/3
1) cos(x)=0,5 => x=±pi/3 +2*pi*n
2) cos(x)=1/3 => x=±arccos(1/3)+2*pi*n
