\[ \boxed { \left ( y \left ( x \right ) \right ) ^{2} \left ( {\frac {\rm d}{{\rm d}x}}y \left ( x \right ) \right ) ^{2}-4\,ay \left ( x \right ) {\frac {\rm d}{{\rm d}x}}y \left ( x \right ) + \left ( y \left ( x \right ) \right ) ^{2}-4\,ax+4\,{a}^{2}=0} \]
Mathematica: cpu = 0.366546 (sec), leaf count = 85 \[ \left \{\left \{y(x)\to -\frac {\sqrt {16 a^3 x-4 a^2 x^2-4 a c_1 x-c_1^2}}{2 a}\right \},\left \{y(x)\to \frac {\sqrt {16 a^3 x-4 a^2 x^2-4 a c_1 x-c_1^2}}{2 a}\right \}\right \} \]
Maple: cpu = 0.905 (sec), leaf count = 113 \[ \left \{ y \left ( x \right ) =-2\,\sqrt {ax},y \left ( x \right ) =2\, \sqrt {ax},y \left ( x \right ) =-{\frac {1}{4\,a}\sqrt {-16\,{a}^{4}+32 \,{a}^{3}x-16\,{a}^{2}{x}^{2}+8\,{\it \_C1}\,{a}^{2}+8\,{\it \_C1}\,ax -{{\it \_C1}}^{2}}},y \left ( x \right ) ={\frac {1}{4\,a}\sqrt {-16\,{a }^{4}+32\,{a}^{3}x-16\,{a}^{2}{x}^{2}+8\,{\it \_C1}\,{a}^{2}+8\,{\it \_C1}\,ax-{{\it \_C1}}^{2}}} \right \} \]