\[
\boxed{
{\frac {\rm d}{{\rm d}x}}y \left( x \right) ={\frac { \left( - \left( y \left( x \right)  \right) ^{2}+4\,ax \right) ^{3}}{ \left( - \left( y \left( x \right)  \right) ^{2}+4\,ax-1 \right) y \left( x \right) }}=0}
\]