\[
\boxed{
 \left\{ {\frac {\rm d}{{\rm d}t}}x \left( t \right) =-y \left( t \right) ,{\frac {\rm d}{{\rm d}t}}y \left( t \right) =2\,x \left( t \right) +2\,y \left( t \right)  \right\} }
\]