\[ a^2 \left (-x^2\right )-2 a^2 x y(x) y'(x)+\left (1-a^2\right ) y(x)^2 y'(x)^2+y(x)^2=0 \] ✓ Mathematica : cpu = 0.40395 (sec), leaf count = 212
\[\left \{\left \{y(x)\to -\frac {\sqrt {a^6 \left (-x^2\right )+3 a^4 x^2-3 a^2 x^2+2 a^2 x e^{a^2 c_1-c_1}-2 x e^{a^2 c_1-c_1}+e^{2 a^2 c_1-2 c_1}+x^2}}{\sqrt {a^6-3 a^4+3 a^2-1}}\right \},\left \{y(x)\to \frac {\sqrt {a^6 \left (-x^2\right )+3 a^4 x^2-3 a^2 x^2+2 a^2 x e^{a^2 c_1-c_1}-2 x e^{a^2 c_1-c_1}+e^{2 a^2 c_1-2 c_1}+x^2}}{\sqrt {a^6-3 a^4+3 a^2-1}}\right \}\right \}\] ✓ Maple : cpu = 0.254 (sec), leaf count = 189
\[\left \{y \left (x \right ) = x \RootOf \left (c_{1}+\int _{}^{\textit {\_Z}}\frac {\left (-\textit {\_a}^{2} a^{2}+\textit {\_a}^{2}-a^{2}+\sqrt {\textit {\_a}^{2} a^{2}-\textit {\_a}^{2}+a^{2}}\right ) \textit {\_a}}{\left (\textit {\_a}^{2} a^{2}-\textit {\_a}^{2}+a^{2}\right ) \left (\textit {\_a}^{2}+1\right )}d \textit {\_a} -\ln \left (x \right )\right ), y \left (x \right ) = x \RootOf \left (c_{1}-\left (\int _{}^{\textit {\_Z}}\frac {\left (\textit {\_a}^{2} a^{2}-\textit {\_a}^{2}+a^{2}+\sqrt {\textit {\_a}^{2} a^{2}-\textit {\_a}^{2}+a^{2}}\right ) \textit {\_a}}{\left (\textit {\_a}^{2} a^{2}-\textit {\_a}^{2}+a^{2}\right ) \left (\textit {\_a}^{2}+1\right )}d \textit {\_a} \right )-\ln \left (x \right )\right ), y \left (x \right ) = \frac {a x}{\sqrt {-a^{2}+1}}, y \left (x \right ) = -\frac {a x}{\sqrt {-a^{2}+1}}\right \}\]