If $\large\frac{dy}{dx}=\frac{x-y}{x+y}$ then

Question

\[\begin{array}{1 1}(1)2xy+y^{2}+x^{2}=c&(2)x^{2}+y^{2}-x+y=c\\(3)x^{2}+y^{2}-2xy=c&(4)x^{2}-y^{2}-2xy=c\end{array}\]