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