\[ x \left (-a+x^2+y(x)^2\right ) y'(x)-y(x) \left (a+x^2+y(x)^2\right )=0 \] ✓ Mathematica : cpu = 0.226574 (sec), leaf count = 71
\[\left \{\left \{y(x)\to \frac {1}{2} \left (c_1 x-\sqrt {-4 a+4 x^2+c_1{}^2 x^2}\right )\right \},\left \{y(x)\to \frac {1}{2} \left (\sqrt {-4 a+4 x^2+c_1{}^2 x^2}+c_1 x\right )\right \}\right \}\] ✓ Maple : cpu = 0.068 (sec), leaf count = 112
\[ \left \{ \left ( \left ( y \left ( x \right ) \right ) ^{-2}- \left ( -{x}^{2}+a \right ) ^{-1} \right ) ^{-1}=-{x\sqrt {{x}^{2}-a}{\frac {1}{\sqrt {{\it \_C1}+4\,{\frac {a}{{x}^{2}-a}}}}}}+{\frac {{x}^{2}}{2}}-{\frac {a}{2}}, \left ( \left ( y \left ( x \right ) \right ) ^{-2}- \left ( -{x}^{2}+a \right ) ^{-1} \right ) ^{-1}={x\sqrt {{x}^{2}-a}{\frac {1}{\sqrt {{\it \_C1}+4\,{\frac {a}{{x}^{2}-a}}}}}}+{\frac {{x}^{2}}{2}}-{\frac {a}{2}} \right \} \]