Cos^2x+cosx-sin^2x=0
Cos^2x+cosx-sin^2x=0 cos^2x+cosx-(1-cos^2x)=0 cos^2x+cosx-1+cos^2x=0 2cos^2x+cosx=0 cosx(2cosx+1)=0 cosx=0 x=П/2+Пn, n∈Z 2cosx+1=0 cosx=-1/2 x=±(П-arccos1/2)+2Пn, n∈Z x=±2П/3+2Пn, n∈Z