\[ \boxed { {\frac {{\rm d}^{2}}{{\rm d}{x}^{2}}}y \left ( x \right ) + \left ( {\frac {\rm d}{{\rm d}x}}y \left ( x \right ) \right ) \tan \left ( x \right ) -y \left ( x \right ) \left ( \cos \left ( x \right ) \right ) ^{2}=0} \]
Mathematica: cpu = 0.032504 (sec), leaf count = 21 \[ \left \{\left \{y(x)\to c_1 \cosh (\sin (x))+i c_2 \sinh (\sin (x))\right \}\right \} \]
Maple: cpu = 0.032 (sec), leaf count = 17 \[ \left \{ y \left ( x \right ) ={\it \_C1}\,{{\rm e}^{\sin \left ( x \right ) }}+{\it \_C2}\,{{\rm e}^{-\sin \left ( x \right ) }} \right \} \]