\[
\boxed{
{\frac {\rm d}{{\rm d}x}}y \left( x \right) ={\frac { \left( x-y \left( x \right)  \right) ^{3} \left( y \left( x \right) +x \right) ^{3}x}{ \left( - \left( y \left( x \right)  \right) ^{2}+{x}^{2}-1 \right) y \left( x \right) }}=0}
\]