\[
\boxed{
 \left\{ {\frac {\rm d}{{\rm d}t}}x \left( t \right) ={\it a1}\,x \left( t \right) +{\it b1}\,y \left( t \right) +{\it c1},{\frac {\rm d}{{\rm d}t}}y \left( t \right) ={\it a2}\,x \left( t \right) +{\it b2}\,y \left( t \right) +{\it c2} \right\} }
\]