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