(2)
\[20\lg K = 20\lg 100 = 40\]
\[\frac{40-x}{\lg 1 - \lg 25} = -20 \Rightarrow x = 40(1-\lg 5)\]
\[\frac{40(1-\lg 5)-0}{\lg 25 - \lg \omega_c} = -40 \Rightarrow \omega_c = 50\]
γ=180°+G(j50)=26.565°
(3)
\[G_c(s) = \frac{1+\dfrac{s}{3.8}}{1+\dfrac{s}{9.1}}\]
超前校正，系统的相角裕量和截止频率提高
(4)
加入超前校正后，会降低系统的超调量，故虚线是校正后系统
九、
(1)
开环奈氏曲线起于实轴，无积分环节
(2)
\[N_+ = N_- = 1, N = N_+ - N_- = 0\]
\[Z = P - 2N = 0\]
系统稳定
(3)
40