\[ \left \{x'(t)=a x(t)-y(t),y'(t)=a y(t)+x(t)\right \} \] ✓ Mathematica : cpu = 0.0040987 (sec), leaf count = 51
\[\left \{\left \{x(t)\to c_1 e^{a t} \cos (t)-c_2 e^{a t} \sin (t),y(t)\to c_2 e^{a t} \cos (t)+c_1 e^{a t} \sin (t)\right \}\right \}\] ✓ Maple : cpu = 0.036 (sec), leaf count = 37
\[ \left \{ \left \{ x \left ( t \right ) ={{\rm e}^{at}} \left ( {\it \_C1}\,\sin \left ( t \right ) +{\it \_C2}\,\cos \left ( t \right ) \right ) ,y \left ( t \right ) ={{\rm e}^{at}} \left ( \sin \left ( t \right ) {\it \_C2}-\cos \left ( t \right ) {\it \_C1} \right ) \right \} \right \} \]