AP8.5 A closed-loop system with unity feedback has a transfer function

(a) Determine the loop transfer function.

(b) Plot the log

arithmic-magnitude versus phase curve, and identify the frequency points for ω equal to 1, 10, 50, 110, and 500.

(c) Is the open-loop system stable? Is the closed-loop sys

tem stable?

T(s) = 20(s+2) s2+18s +40