\[ \sin (2 x) y'(x)+\sin (2 y(x))=0 \] ✓ Mathematica : cpu = 0.215688 (sec), leaf count = 15
\[\left \{\left \{y(x)\to \cot ^{-1}\left (e^{-2 c_1} \tan (x)\right )\right \}\right \}\] ✓ Maple : cpu = 0.187 (sec), leaf count = 105
\[y \relax (x ) = \frac {\arctan \left (-\frac {2 c_{1} \left (\sin \left (4 x \right )+2 \sin \left (2 x \right )\right )}{c_{1}^{2} \cos \left (4 x \right )-c_{1}^{2}-\cos \left (4 x \right )-4 \cos \left (2 x \right )-3}, \frac {c_{1}^{2} \cos \left (4 x \right )-c_{1}^{2}+\cos \left (4 x \right )+4 \cos \left (2 x \right )+3}{c_{1}^{2} \cos \left (4 x \right )-c_{1}^{2}-\cos \left (4 x \right )-4 \cos \left (2 x \right )-3}\right )}{2}\]