\[ \boxed { {\frac {{\rm d}^{2}}{{\rm d}{x}^{2}}}y \left ( x \right ) ={\frac {\cos \left ( 2\,x \right ) {\frac {\rm d}{{\rm d}x}}y \left ( x \right ) }{\sin \left ( 2\,x \right ) }}-2\,y \left ( x \right ) =0} \]
Mathematica: cpu = 0.202526 (sec), leaf count = 80 \[ \left \{\left \{y(x)\to c_1 \left (\cos ^2(x)-\frac {1}{2}\right )-\frac {2}{3} c_2 \cos ^{\frac {3}{2}}(x) \left (2 \cos ^2(x) \, _2F_1\left (\frac {1}{4},\frac {3}{4};\frac {7}{4};\cos ^2(x)\right )-\, _2F_1\left (\frac {1}{4},\frac {3}{4};\frac {7}{4};\cos ^2(x)\right )+3 \left (1-\cos ^2(x)\right )^{3/4}\right )\right \}\right \} \]
Maple: cpu = 0.156 (sec), leaf count = 35 \[ \left \{ y \left ( x \right ) ={\it \_C1}\, \left ( \sin \left ( 2\,x \right ) \right ) ^{{\frac {3}{4}}}{\it LegendreP} \left ( {\frac {1}{4 }},{\frac {3}{4}},\cos \left ( 2\,x \right ) \right ) +{\it \_C2}\, \left ( \sin \left ( 2\,x \right ) \right ) ^{{\frac {3}{4}}}{\it LegendreQ} \left ( {\frac {1}{4}},{\frac {3}{4}},\cos \left ( 2\,x \right ) \right ) \right \} \]