\[
\boxed{
 \left\{ {\frac {{\rm d}^{2}}{{\rm d}{t}^{2}}}x \left( t \right) +a \left( {\frac {\rm d}{{\rm d}t}}x \left( t \right) -{\frac {\rm d}{{\rm d}t}}y \left( t \right)  \right) +{\it b1}\,x \left( t \right) ={\it c1}\,{{\rm e}^{i\omega\,t}},{\frac {{\rm d}^{2}}{{\rm d}{t}^{2}}}y \left( t \right) +a \left( {\frac {\rm d}{{\rm d}t}}y \left( t \right) -{\frac {\rm d}{{\rm d}t}}x \left( t \right)  \right) +{\it b2}\,y \left( t \right) ={\it c2}\,{{\rm e}^{i\omega\,t}} \right\} }
\]