\[ y'(x) \cos (y(x)) (\cos (y(x))-\sin (\alpha ) \sin (x))+\cos (x) (\cos (x)-\sin (\alpha ) \sin (y(x)))=0 \] ✓ Mathematica : cpu = 0.607159 (sec), leaf count = 43
\[\text {Solve}\left [4 \sin (\alpha ) \sin (x) \sin (y(x))-4 \left (\frac {y(x)}{2}+\frac {1}{4} \sin (2 y(x))\right )-2 x-\sin (2 x)=c_1,y(x)\right ]\] ✓ Maple : cpu = 0.43 (sec), leaf count = 33
\[\left \{\frac {\cos \left (x \right ) \sin \left (x \right )}{2}+c_{1}+\frac {x}{2}+\frac {\left (-2 \sin \left (\alpha \right ) \sin \left (x \right )+\cos \left (y \left (x \right )\right )\right ) \sin \left (y \left (x \right )\right )}{2}+\frac {y \left (x \right )}{2} = 0\right \}\]