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