\[ y''(x)-\cot (x) y'(x)+y(x) \sin ^2(x)=0 \] ✓ Mathematica : cpu = 0.0370826 (sec), leaf count = 19
\[\left \{\left \{y(x)\to c_1 \cos (\cos (x))-c_2 \sin (\cos (x))\right \}\right \}\]
✓ Maple : cpu = 0.164 (sec), leaf count = 15
\[ \left \{ y \left ( x \right ) ={\it \_C1}\,\sin \left ( \cos \left ( x \right ) \right ) +{\it \_C2}\,\cos \left ( \cos \left ( x \right ) \right ) \right \} \]