6cos^2x+5cos(π/2-x)-7=0
6cos^2+5sinx-7=0
6(1-sin^2x)+5sinx-7=0
6-6sin^2x+5sinx-7=0
-6sin^2x+5sinx-1=0
6sin^2x-5sinx+1=0
sinx=t t по модулю≤1
6t^2-5t+1=0
D=25-4*6*1=1
t1= 5+1/12=1/2
t2=5-1/12=1/3
sinx=1/2 sinx=1/3
x=π/6+2πn;n∈z x=arcsin1/3+2πn;n∈z
x=5π/6+2πn;n∈z x=π-arcsin1/3+2πn;n∈z