\[
\boxed{
{\frac {{\rm d}^{2}}{{\rm d}{x}^{2}}}y \left( x \right) + \left( y \left( x \right)  \right) ^{3}{\frac {\rm d}{{\rm d}x}}y \left( x \right) -y \left( x \right)  \left( {\frac {\rm d}{{\rm d}x}}y \left( x \right)  \right) \sqrt { \left( y \left( x \right)  \right) ^{4}+4\,{\frac {\rm d}{{\rm d}x}}y \left( x \right) }=0}
\]