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