\[ -\sin (x) y'(x)+(2 \cos (x)+1) y''(x)+y^{(3)}(x) \sin (x)-\cos (x)=0 \] ✓ Mathematica : cpu = 0.840875 (sec), leaf count = 72
\[\left \{\left \{y(x)\to \frac {\sin \left (\frac {x}{2}\right ) \left (-2 \cos \left (\frac {x}{2}\right ) \sin ^{-1}(\cos (x))+\sqrt {2} \left (c_2 x \sin \left (\frac {x}{2}\right )+\cos \left (\frac {x}{2}\right ) (c_2 \log (2 (\cos (x)+1))+2 c_1)\right )\right )}{\cos (x)-1}+c_3\right \}\right \}\] ✓ Maple : cpu = 0.392 (sec), leaf count = 74
\[ \left \{ y \left ( x \right ) ={\frac {1}{\sin \left ( x \right ) \left ( -1+\cos \left ( x \right ) \right ) } \left ( - \left ( \sin \left ( x \right ) \right ) ^{2}\ln \left ( {\frac {1-\cos \left ( x \right ) }{\sin \left ( x \right ) }} \right ) {\it \_C1}+ \left ( \sin \left ( x \right ) \right ) ^{2}\ln \left ( \sin \left ( x \right ) \right ) {\it \_C1}+ \left ( \sin \left ( x \right ) \right ) ^{2}{\it \_C3}- \left ( -1+\cos \left ( x \right ) \right ) \left ( {\it \_C1}\,x-{\it \_C2}-1 \right ) \sin \left ( x \right ) - \left ( \cos \left ( x \right ) \right ) ^{2}x+x \right ) } \right \} \]