\[ y'(x)=\frac {\frac {1}{2} x^2 \cos (2 y(x))+\frac {x^2}{2}-\frac {1}{2} \sin (2 y(x))}{x} \] ✓ Mathematica : cpu = 0.362642 (sec), leaf count = 23
\[\left \{\left \{y(x)\to \tan ^{-1}\left (\frac {2 x^3+3 c_1}{6 x}\right )\right \}\right \}\] ✓ Maple : cpu = 0.422 (sec), leaf count = 17
\[\left \{y \left (x \right ) = \arctan \left (\frac {x^{3}+6 c_{1}}{3 x}\right )\right \}\]