\[ \sqrt {a^2+x^2} y'(x)-\sqrt {a^2+x^2}+y(x)+x=0 \] ✗ Mathematica : cpu = 299.997 (sec), leaf count = 0 , timed out
$Aborted
✓ Maple : cpu = 0.018 (sec), leaf count = 36
\[ \left \{ y \left ( x \right ) ={1 \left ( {a}^{2}\ln \left ( x+\sqrt {{a}^{2}+{x}^{2}} \right ) +{\it \_C1} \right ) \left ( x+\sqrt {{a}^{2}+{x}^{2}} \right ) ^{-1}} \right \} \]