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