The solution of $(x^2+y^2)dx =2xy \;dy$ is :

Question

\[\begin {array} {1 1} (a)\;c(x^2-y^2)=x & \quad (b)\;c(x^2+y^2)=x \\ (c)\;c(x^2-y^2)=y & \quad (d)\;c(x^2+y^2)=y \end {array}\]