\[ \boxed { 3\, \left ( {\frac {\rm d}{{\rm d}x}}y \left ( x \right ) \right ) \sin \left ( x \right ) \sin \left ( y \left ( x \right ) \right ) +5\, \left ( \cos \left ( x \right ) \right ) ^{4}y \left ( x \right ) =0} \]
Mathematica: cpu = 0.055507 (sec), leaf count = 45 \[ \left \{\left \{y(x)\to \text {SinIntegral}^{(-1)}\left (c_1-\frac {5}{3} \left (\frac {5 \cos (x)}{4}+\frac {1}{12} \cos (3 x)+\log \left (\sin \left (\frac {x}{2}\right )\right )-\log \left (\cos \left (\frac {x}{2}\right )\right )\right )\right )\right \}\right \} \]
Maple: cpu = 0.047 (sec), leaf count = 28 \[ \left \{ {\frac {\cos \left ( 3\,x \right ) }{12}}+{\frac {5\,\cos \left ( x \right ) }{4}}+\ln \left ( \csc \left ( x \right ) -\cot \left ( x \right ) \right ) +{\frac {3\,{\it Si} \left ( y \left ( x \right ) \right ) }{5}}+{\it \_C1}=0 \right \} \]