dsolve({diff(diff(x(t),t),t)+a*(diff(x(t),t)-diff(y(t),t))+b1*x(t) = c1*exp(I*omega*t), diff(diff(y(t),t),t)+a*(diff(y(t),t)-diff(x(t),t))+b2*y(t) = c2*exp(I*omega*t)})