\[ -a^2+y(x)^2 y'(x)^2+y(x)^2=0 \] ✓ Mathematica : cpu = 0.065371 (sec), leaf count = 117
\[\left \{\left \{y(x)\to -\sqrt {a^2-x^2-2 c_1 x-c_1{}^2}\right \},\left \{y(x)\to \sqrt {a^2-x^2-2 c_1 x-c_1{}^2}\right \},\left \{y(x)\to -\sqrt {a^2-x^2+2 c_1 x-c_1{}^2}\right \},\left \{y(x)\to \sqrt {a^2-x^2+2 c_1 x-c_1{}^2}\right \}\right \}\] ✓ Maple : cpu = 0.246 (sec), leaf count = 54
\[\left \{y \left (x \right ) = a, y \left (x \right ) = \sqrt {a^{2}-x^{2}+2 c_{1} x -c_{1}^{2}}, y \left (x \right ) = -a, y \left (x \right ) = -\sqrt {\left (-c_{1}+a +x \right ) \left (c_{1}+a -x \right )}\right \}\]