\[ \left (x^2-a^2\right ) y'(x)^2-x^2-2 x y(x) y'(x)=0 \] ✓ Mathematica : cpu = 0.369148 (sec), leaf count = 26
\[\left \{\left \{y(x)\to \frac {a^2-x^2+c_1{}^2}{2 c_1}\right \}\right \}\] ✓ Maple : cpu = 0.727 (sec), leaf count = 51
\[\left \{y \left (x \right ) = \sqrt {a^{2}-x^{2}}, y \left (x \right ) = -\sqrt {a^{2}-x^{2}}, y \left (x \right ) = -c_{1} a^{2}+c_{1} x^{2}-\frac {1}{4 c_{1}}\right \}\]