It seems correct to me...
$$y'-y\tan(x)=-2\sin(x)$$ $$y'-y\frac {\sin(x)}{\cos(x)}=-2\sin(x)$$ $$\frac {y'\cos(x)-y\sin(x)}{\cos(x)}=-2\sin(x)$$ $$({y}{\cos(x)})'=-\sin(2x)$$ Integrating .. $${y(x)}{\cos(x)}=-\int \sin(2x) dx$$ $$y(x)=\frac 1 {\cos(x)}(\frac {\cos(2x)}2+K)$$
The same answer as yours.....with $\cos(2x)=2cos^2(x)-1$
$$\boxed {y(x)=\frac C {\cos(x)}+\cos(x)}$$