\[
\boxed{
a{x}^{3} \left( {\frac {\rm d}{{\rm d}x}}y \left( x \right)  \right) {\frac {{\rm d}^{2}}{{\rm d}{x}^{2}}}y \left( x \right) +b \left( y \left( x \right)  \right) ^{2}=0}
\]