\[ \sin (2 x) y'(x)+\sin (2 y(x))=0 \] ✓ Mathematica : cpu = 0.203055 (sec), leaf count = 15
\[\left \{\left \{y(x)\to \cot ^{-1}\left (e^{-2 c_1} \tan (x)\right )\right \}\right \}\] ✓ Maple : cpu = 0.142 (sec), leaf count = 102
\[ \left \{ y \left ( x \right ) ={\frac {1}{2}\arctan \left ( 2\,{\frac {{\it \_C1}\, \left ( \sin \left ( 4\,x \right ) +2\,\sin \left ( 2\,x \right ) \right ) }{-{{\it \_C1}}^{2}\cos \left ( 4\,x \right ) +{{\it \_C1}}^{2}+4\,\cos \left ( 2\,x \right ) +\cos \left ( 4\,x \right ) +3}},{\frac {{{\it \_C1}}^{2}\cos \left ( 4\,x \right ) -{{\it \_C1}}^{2}+4\,\cos \left ( 2\,x \right ) +\cos \left ( 4\,x \right ) +3}{{{\it \_C1}}^{2}\cos \left ( 4\,x \right ) -{{\it \_C1}}^{2}-4\,\cos \left ( 2\,x \right ) -\cos \left ( 4\,x \right ) -3}} \right ) } \right \} \]