\[
\boxed{
{\frac {\rm d}{{\rm d}x}}y \left( x \right) =-1/2\,{\frac { \left( \sqrt {a}{x}^{4}+\sqrt {a}{x}^{3}-2\,\sqrt {a{x}^{4}+8\,y \left( x \right) } \right) \sqrt {a}}{1+x}}=0}
\]