\[ y''(x)+\tan (x) y'(x)-y(x) \cos ^2(x)=0 \] ✓ Mathematica : cpu = 0.0277072 (sec), leaf count = 21
\[\{\{y(x)\to c_1 \cosh (\sin (x))+i c_2 \sinh (\sin (x))\}\}\] ✓ Maple : cpu = 0.053 (sec), leaf count = 17
\[\{y \left (x \right ) = c_{1} {\mathrm e}^{\sin \left (x \right )}+c_{2} {\mathrm e}^{-\sin \left (x \right )}\}\]