\[ \left (x^2-a^2\right ) y'(x)^2-x^2-2 x y(x) y'(x)=0 \] ✓ Mathematica : cpu = 0.456419 (sec), leaf count = 26
\[\left \{\left \{y(x)\to \frac {a^2+c_1^2-x^2}{2 c_1}\right \}\right \}\]
✓ Maple : cpu = 0.738 (sec), leaf count = 51
\[ \left \{ y \left ( x \right ) =\sqrt {{a}^{2}-{x}^{2}},y \left ( x \right ) =-\sqrt {{a}^{2}-{x}^{2}},y \left ( x \right ) ={\it \_C1}\,{x}^{2}-{\it \_C1}\,{a}^{2}-{\frac {1}{4\,{\it \_C1}}} \right \} \]