\left\{\text{a11} x''(t)+\text{a12} y''(t)+\text{b11} x'(t)+\text{b12} y'(t)+\text{c11} x(t)+\text{c12} y(t)=0,\text{a21} x''(t)+\text{a22} y''(t)+\text{b21} x'(t)+\text{b22} y'(t)+\text{c21} x(t)+\text{c22} y(t)=0\right\}