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