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