Hãy xác định H ( Z ) trong hệ thống sau

$H\left(Z\right)=H{}_1\left(Z\right)+H{}_2\left(Z\right)$

$H\left(Z\right)=\frac{H{}_1\left(Z\right)}{1-H{}_2\left(Z\right)\cdot H{}_1\left(Z\right)}$

$\text{H}\left(\text{Z}\right)=\text{H}{}_1\left(\text{Z}\right)-\text{H}{}_2\left(\text{Z}\right)$

$H\left(Z\right)=\frac{H{}_1\left(Z\right)}{1+H{}_2\left(Z\right)}$