\[ \boxed { x{\frac {\rm d}{{\rm d}x}}y \left ( x \right ) -x\sqrt { \left ( \left ( y \left ( x \right ) \right ) ^{2}-{x}^{2} \right ) \left ( \left ( y \left ( x \right ) \right ) ^{2}-4\,{x}^{2} \right ) }-y \left ( x \right ) =0} \]
Mathematica: cpu = 0.410552 (sec), leaf count = 143 \[ \text {Solve}\left [\frac {2 \left (\frac {y(x)}{x}-2\right )^{3/2} \sqrt {-\frac {4}{\frac {y(x)}{x}-2}-1} \sqrt {-\frac {3}{\frac {y(x)}{x}-2}-1} \sqrt {\frac {1}{\frac {y(x)}{x}-2}+1} F\left (\left .\sin ^{-1}\left (\frac {\sqrt {-1-\frac {3}{\frac {y(x)}{x}-2}}}{\sqrt {2}}\right )\right |-8\right )}{\sqrt {\frac {y(x)}{x}-1} \sqrt {\frac {y(x)}{x}+1} \sqrt {\frac {y(x)}{x}+2}}=c_1+\frac {x^2}{2},y(x)\right ] \]
Maple: cpu = 0.156 (sec), leaf count = 144 \[ \left \{ \int _{{\it \_b}}^{x}\!{1 \left ( {\it \_a}\,\sqrt {4\,{{\it \_a}}^{4}-5\,{{\it \_a}}^{2} \left ( y \left ( x \right ) \right ) ^{2}+ \left ( y \left ( x \right ) \right ) ^{4}}+y \left ( x \right ) \right ) {\frac {1}{\sqrt {4\,{{\it \_a}}^{4}-5\,{{\it \_a}}^{2} \left ( y \left ( x \right ) \right ) ^{2}+ \left ( y \left ( x \right ) \right ) ^{ 4}}}}}\,{\rm d}{\it \_a}+\int ^{y \left ( x \right ) }\!-{1 \left ( \int _ {{\it \_b}}^{x}\!{(4\,{{\it \_a}}^{4}-{{\it \_f}}^{4}) \left ( 4\,{{ \it \_a}}^{4}-5\,{{\it \_a}}^{2}{{\it \_f}}^{2}+{{\it \_f}}^{4} \right ) ^{-{\frac {3}{2}}}}\,{\rm d}{\it \_a}\sqrt {{{\it \_f}}^{4}-5 \,{{\it \_f}}^{2}{x}^{2}+4\,{x}^{4}}+x \right ) {\frac {1}{\sqrt {{{ \it \_f}}^{4}-5\,{{\it \_f}}^{2}{x}^{2}+4\,{x}^{4}}}}}{d{\it \_f}}+{ \it \_C1}=0 \right \} \]