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