\[ f\left (x^2+y(x)^2\right ) \sqrt {y'(x)^2+1}-x y'(x)+y(x)=0 \] ✗ Mathematica : cpu = 300.002 (sec), leaf count = 0 , timed out
$Aborted
✓ Maple : cpu = 2.066 (sec), leaf count = 50
\[ \left \{ y \left ( x \right ) ={x \left ( \tan \left ( {\it RootOf} \left ( -2\,{\it \_Z}+\int ^{{\frac {{x}^{2} \left ( \left ( \tan \left ( {\it \_Z} \right ) \right ) ^{2}+1 \right ) }{ \left ( \tan \left ( {\it \_Z} \right ) \right ) ^{2}}}}\!{\frac {f \left ( {\it \_a} \right ) }{{\it \_a}}{\frac {1}{\sqrt {- \left ( f \left ( {\it \_a} \right ) \right ) ^{2}+{\it \_a}}}}}{d{\it \_a}}+2\,{\it \_C1} \right ) \right ) \right ) ^{-1}} \right \} \]