sin2x-9sinxcosx+3cos2x=-1 Прошу помощи

Sin2x-9sinxcosx+3cos2x=12sin (x) cos (x) -9sin (x) cos (x)+3 (cos^2 (x) -sin^2 (x)=cos^2 (x)+sin^2 (x) -7sin (x) cos (x)+2cos^2 (x) -4sin^2 (x)=02cos^2 (x) -7sin (x) cos (x) -4sin^2 (x)=0- (sin (x)+2cos (x) (4sin (x) -cos (x)=0Получаем два случая: sin (x)+2cos (x)=0 => sin (x) /cos (x)=-2 => tg (x)=-2 => x=arctg (-2)+pi*nи 4sin (x) -cos (x)=0 => sin (x) /cos (x)=1/4 => tg (x)=1/4 => x=arctg (1/4)+pi*n