\[ \sqrt {a^2+x^2} y'(x)-\sqrt {a^2+x^2}+y(x)+x=0 \] ✓ Mathematica : cpu = 0.029563 (sec), leaf count = 42
\[\left \{\left \{y(x)\to \frac {a^2 \log \left (\sqrt {a^2+x^2}+x\right )+c_1}{\sqrt {a^2+x^2}+x}\right \}\right \}\]
✓ Maple : cpu = 0.019 (sec), leaf count = 36
\[ \left \{ y \left ( x \right ) ={1 \left ( {a}^{2}\ln \left ( x+\sqrt {{a}^{2}+{x}^{2}} \right ) +{\it \_C1} \right ) \left ( x+\sqrt {{a}^{2}+{x}^{2}} \right ) ^{-1}} \right \} \]