\[ \boxed { {\frac {\rm d}{{\rm d}x}}y \left ( x \right ) =1/2\,{\frac {-\sin \left ( 2\,y \left ( x \right ) \right ) +\cos \left ( 2\,y \left ( x \right ) \right ) {x}^{3}+{x}^{3}}{x}}=0} \]
Mathematica: cpu = 0.080010 (sec), leaf count = 21 \[ \left \{\left \{y(x)\to \tan ^{-1}\left (\frac {2 c_1+x^4}{4 x}\right )\right \}\right \} \]
Maple: cpu = 0.499 (sec), leaf count = 17 \[ \left \{ y \left ( x \right ) =\arctan \left ( {\frac {{x}^{4}+8\,{\it \_C1}}{4\,x}} \right ) \right \} \]