\[ -x \sqrt {\left (y(x)^2-4 x^2\right ) \left (y(x)^2-x^2\right )}+x y'(x)-y(x)=0 \] ✓ Mathematica : cpu = 0.547666 (sec), leaf count = 121
DSolve[-y[x] - x*Sqrt[(-4*x^2 + y[x]^2)*(-x^2 + y[x]^2)] + x*Derivative[1][y][x] == 0,y[x],x]
\[\text {Solve}\left [\frac {\sqrt {\frac {\frac {y(x)}{x}+2}{\frac {y(x)}{x}-1}} \sqrt {\frac {\frac {y(x)}{x}+1}{\frac {2 y(x)}{x}+4}} F\left (\sin ^{-1}\left (\sqrt {\frac {2}{3}} \sqrt {\frac {\frac {y(x)}{x}-2}{\frac {y(x)}{x}-1}}\right )|\frac {9}{8}\right )}{\sqrt {\frac {\frac {y(x)}{x}+1}{\frac {y(x)}{x}-1}}}=\frac {x^2}{2}+c_1,y(x)\right ]\] ✓ Maple : cpu = 0.229 (sec), leaf count = 86
dsolve(x*diff(y(x),x)-x*((y(x)^2-x^2)*(y(x)^2-4*x^2))^(1/2)-y(x) = 0,y(x))
\[\int _{\textit {\_b}}^{x}\frac {\textit {\_a} \sqrt {4 \textit {\_a}^{4}-5 \textit {\_a}^{2} y \left (x \right )^{2}+y \left (x \right )^{4}}+y \left (x \right )}{\sqrt {4 \textit {\_a}^{4}-5 \textit {\_a}^{2} y \left (x \right )^{2}+y \left (x \right )^{4}}}d \textit {\_a} +\int _{}^{y \left (x \right )}-\frac {\textit {\_b}}{\sqrt {4 \textit {\_b}^{4}-5 \textit {\_b}^{2} \textit {\_f}^{2}+\textit {\_f}^{4}}}d \textit {\_f} +c_{1} = 0\]