\[
\boxed{
{\frac {\rm d}{{\rm d}x}}y \left( x \right) ={\frac {-{b}^{3}+6\,{b}^{2}x-12\,b{x}^{2}+8\,{x}^{3}-4\,b \left( y \left( x \right)  \right) ^{2}+8\,x \left( y \left( x \right)  \right) ^{2}+8\, \left( y \left( x \right)  \right) ^{3}}{ \left( 2\,x-b \right) ^{3}}}=0}
\]