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