\[
\boxed{
 \left(  \left( y \left( x \right)  \right) ^{2}+{x}^{2} \right) f \left( {\frac {y \left( x \right) }{\sqrt { \left( y \left( x \right)  \right) ^{2}+{x}^{2}}}} \right)  \left(  \left( {\frac {\rm d}{{\rm d}x}}y \left( x \right)  \right) ^{2}+1 \right) - \left( x{\frac {\rm d}{{\rm d}x}}y \left( x \right) -y \left( x \right)  \right) ^{2}=0}
\]