\[ x^2 \left (x^2-a^2\right ) y'(x)^2-1=0 \] ✓ Mathematica : cpu = 0.0205922 (sec), leaf count = 120
\[\left \{\left \{y(x)\to -\frac {x \sqrt {x^2-a^2} \tan ^{-1}\left (\frac {\sqrt {x^2-a^2}}{a}\right )}{a \sqrt {x^4-a^2 x^2}}+c_1\right \},\left \{y(x)\to \frac {x \sqrt {x^2-a^2} \tan ^{-1}\left (\frac {\sqrt {x^2-a^2}}{a}\right )}{a \sqrt {x^4-a^2 x^2}}+c_1\right \}\right \}\] ✓ Maple : cpu = 0.154 (sec), leaf count = 90
\[ \left \{ y \left ( x \right ) =-{\ln \left ( {\frac {1}{x} \left ( -2\,{a}^{2}+2\,\sqrt {-{a}^{2}}\sqrt {-{a}^{2}+{x}^{2}} \right ) } \right ) {\frac {1}{\sqrt {-{a}^{2}}}}}+{\it \_C1},y \left ( x \right ) ={\ln \left ( {\frac {1}{x} \left ( -2\,{a}^{2}+2\,\sqrt {-{a}^{2}}\sqrt {-{a}^{2}+{x}^{2}} \right ) } \right ) {\frac {1}{\sqrt {-{a}^{2}}}}}+{\it \_C1} \right \} \]