\[ \left (a+x y'(x)\right )^2-2 a y(x)+x^2=0 \] ✓ Mathematica : cpu = 1.27785 (sec), leaf count = 70
\[\text {Solve}\left [\left \{y(x)=\frac {2 a x K[1]+x^2 K[1]^2+a^2+x^2}{2 a},x=-\frac {a \sinh ^{-1}(K[1])}{\sqrt {K[1]^2+1}}+\frac {c_1}{\sqrt {K[1]^2+1}}\right \},\{y(x),K[1]\}\right ]\] ✓ Maple : cpu = 10.385 (sec), leaf count = 242
\[\left \{y \left (x \right ) = \frac {-2 \left (a \arcsinh \left (\RootOf \left (-\textit {\_Z}^{2} x^{2}+a^{2} \arcsinh \left (\textit {\_Z} \right )^{2}-2 c_{1} a \arcsinh \left (\textit {\_Z} \right )+c_{1}^{2}-x^{2}\right )\right )-c_{1}\right ) \sqrt {\RootOf \left (-\textit {\_Z}^{2} x^{2}+a^{2} \arcsinh \left (\textit {\_Z} \right )^{2}-2 c_{1} a \arcsinh \left (\textit {\_Z} \right )+c_{1}^{2}-x^{2}\right )^{2}+1}\, a \RootOf \left (-\textit {\_Z}^{2} x^{2}+a^{2} \arcsinh \left (\textit {\_Z} \right )^{2}-2 c_{1} a \arcsinh \left (\textit {\_Z} \right )+c_{1}^{2}-x^{2}\right )+\left (\RootOf \left (-\textit {\_Z}^{2} x^{2}+a^{2} \arcsinh \left (\textit {\_Z} \right )^{2}-2 c_{1} a \arcsinh \left (\textit {\_Z} \right )+c_{1}^{2}-x^{2}\right )^{2}+1\right ) \left (x^{2} \RootOf \left (-\textit {\_Z}^{2} x^{2}+a^{2} \arcsinh \left (\textit {\_Z} \right )^{2}-2 c_{1} a \arcsinh \left (\textit {\_Z} \right )+c_{1}^{2}-x^{2}\right )^{2}+a^{2}+x^{2}\right )}{2 \left (\RootOf \left (-\textit {\_Z}^{2} x^{2}+a^{2} \arcsinh \left (\textit {\_Z} \right )^{2}-2 c_{1} a \arcsinh \left (\textit {\_Z} \right )+c_{1}^{2}-x^{2}\right )^{2}+1\right ) a}\right \}\]