\[
\boxed{
{\frac {\rm d}{{\rm d}x}}y \left( x \right) =-F \left( x \right)  \left( -a{x}^{2}+ \left( y \left( x \right)  \right) ^{2} \right) +{\frac {y \left( x \right) }{x}}=0}
\]