dsolve({a11*diff(diff(x(t),t),t)+b11*diff(x(t),t)+c11*x(t)+a12*diff(diff(y(t),t),t)+b12*diff(y(t),t)+c12*y(t) = 0, a21*diff(diff(x(t),t),t)+b21*diff(x(t),t)+c21*x(t)+a22*diff(diff(y(t),t),t)+b22*diff(y(t),t)+c22*y(t) = 0})