\[ x y'(x)-\sqrt {a^2-x^2}=0 \] ✓ Mathematica : cpu = 0.0323603 (sec), leaf count = 48
\[\left \{\left \{y(x)\to \sqrt {a^2-x^2}-a \log \left (a \sqrt {a^2-x^2}+a^2\right )+a \log (x)+c_1\right \}\right \}\]
✓ Maple : cpu = 0.016 (sec), leaf count = 56
\[ \left \{ y \left ( x \right ) =\sqrt {{a}^{2}-{x}^{2}}-{{a}^{2}\ln \left ( {\frac {1}{x} \left ( 2\,{a}^{2}+2\,\sqrt {{a}^{2}}\sqrt {{a}^{2}-{x}^{2}} \right ) } \right ) {\frac {1}{\sqrt {{a}^{2}}}}}+{\it \_C1} \right \} \]