\[ \boxed { {\frac {{\rm d}^{2}}{{\rm d}{x}^{2}}}y \left ( x \right ) ={\frac { \left ( 3\, \left ( \sin \left ( x \right ) \right ) ^{2}+1 \right ) {\frac {\rm d}{{\rm d}x}}y \left ( x \right ) }{\cos \left ( x \right ) \sin \left ( x \right ) }}+{\frac {y \left ( x \right ) \left ( \sin \left ( x \right ) \right ) ^{2}}{ \left ( \cos \left ( x \right ) \right ) ^{2}}}=0} \]
Mathematica: cpu = 0.240531 (sec), leaf count = 44 \[ \left \{\left \{y(x)\to c_1 \cos ^{\frac {\sqrt {13}}{2}-\frac {3}{2}}(x)+c_2 \cos ^{-\frac {3}{2}-\frac {\sqrt {13}}{2}}(x)\right \}\right \} \]
Maple: cpu = 0.125 (sec), leaf count = 29 \[ \left \{ y \left ( x \right ) ={\it \_C1}\, \left ( \cos \left ( x \right ) \right ) ^{-{\frac {3}{2}}+{\frac {\sqrt {13}}{2}}}+{\it \_C2 }\, \left ( \cos \left ( x \right ) \right ) ^{-{\frac {3}{2}}-{\frac { \sqrt {13}}{2}}} \right \} \]