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