\[0-20\lg\frac{0.5}{0.05}=-20\]
\[0-20\lg\frac{0.5}{0.05}+20\lg\frac{10}{2}=-6\]
(3)
\[G=\dfrac{50\left(\dfrac{s}{0.5}+1\right)}{s\left(\dfrac{s}{0.05}+1\right)\left(\dfrac{s}{10}+1\right)\left(\dfrac{s}{20}+1\right)}\]
由图可见剪切频率为5
相位裕度：\(\gamma=180°-90°+arctg\dfrac{\omega_c}{0.5}-arctg\dfrac{\omega_c}{0.05}-arctg\dfrac{\omega_c}{10}-arctg\dfrac{\omega_c}{20}\)