\[ y''(x)=-4 y(x) \sin (3 x) \csc ^3(x) \] ✓ Mathematica : cpu = 0.121323 (sec), leaf count = 70
\[\left \{\left \{y(x)\to c_1 \sqrt [4]{\cos ^2(x)-1} P_{-\frac {1}{2}+4 i}^{\frac {i \sqrt {47}}{2}}(\cos (x))+c_2 \sqrt [4]{\cos ^2(x)-1} Q_{-\frac {1}{2}+4 i}^{\frac {i \sqrt {47}}{2}}(\cos (x))\right \}\right \}\] ✓ Maple : cpu = 0.502 (sec), leaf count = 38
\[ \left \{ y \left ( x \right ) =\sqrt {\sin \left ( x \right ) } \left ( {\it LegendreQ} \left ( -{\frac {1}{2}}+4\,i,{\frac {i}{2}}\sqrt {47},\cos \left ( x \right ) \right ) {\it \_C2}+{\it LegendreP} \left ( -{\frac {1}{2}}+4\,i,{\frac {i}{2}}\sqrt {47},\cos \left ( x \right ) \right ) {\it \_C1} \right ) \right \} \]