\[ \left \{x'(t)=x(t) \cos (t),y'(t)=x(t) e^{-\sin (t)}\right \} \] ✓ Mathematica : cpu = 0.0164845 (sec), leaf count = 39
\[\left \{\left \{x(t)\to c_1 e^{\sin (t)},y(t)\to c_1 \int _1^te^{\sin (K[1])-\sin (K[1])}dK[1]+c_2\right \}\right \}\] ✓ Maple : cpu = 0.308 (sec), leaf count = 18
\[ \left \{ \left \{ x \left ( t \right ) ={\it \_C2}\,{{\rm e}^{\sin \left ( t \right ) }},y \left ( t \right ) ={\it \_C2}\,t+{\it \_C1} \right \} \right \} \]