\[ y''(x)+\tan (x) y'(x)-y(x) \cos ^2(x)=0 \] ✓ Mathematica : cpu = 0.0345519 (sec), leaf count = 21
\[\left \{\left \{y(x)\to c_1 \cosh (\sin (x))+i c_2 \sinh (\sin (x))\right \}\right \}\]
✓ Maple : cpu = 0.061 (sec), leaf count = 17
\[ \left \{ y \left ( x \right ) ={\it \_C1}\,{{\rm e}^{\sin \left ( x \right ) }}+{\it \_C2}\,{{\rm e}^{-\sin \left ( x \right ) }} \right \} \]