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