\[ y'(x)=\frac {\frac {1}{2} x^2 \cos (2 y(x))+\frac {x^2}{2}-\frac {1}{2} \sin (2 y(x))}{x} \] ✓ Mathematica : cpu = 0.0876103 (sec), leaf count = 23
\[\left \{\left \{y(x)\to \tan ^{-1}\left (\frac {3 c_1+2 x^3}{6 x}\right )\right \}\right \}\] ✓ Maple : cpu = 0.439 (sec), leaf count = 17
\[ \left \{ y \left ( x \right ) =\arctan \left ( {\frac {{x}^{3}+6\,{\it \_C1}}{3\,x}} \right ) \right \} \]