\[ \boxed { x{\frac {\rm d}{{\rm d}x}}y \left ( x \right ) +a\sqrt { \left ( y \left ( x \right ) \right ) ^{2}+{x}^{2}}-y \left ( x \right ) =0} \]
Mathematica: cpu = 0.022503 (sec), leaf count = 16 \[ \left \{\left \{y(x)\to x \sinh \left (c_1-a \log (x)\right )\right \}\right \} \]
Maple: cpu = 0.015 (sec), leaf count = 33 \[ \left \{ {\frac {{x}^{a}}{x}\sqrt { \left ( y \left ( x \right ) \right ) ^{2}+{x}^{2}}}+{\frac {{x}^{a}y \left ( x \right ) }{x}}-{\it \_C1}=0 \right \} \]