9. Using the value of K in Problem 8, compute the gain and phase margins when Td = 0.2.

a. G M. . = 14 dB, P M. . = 27°

b. G M. . = 20 dB, P M. . = 64.9°

c. G M. . = ∞ dB, P M. . = 60°

d. Closed-loop system is unstable

For Problems 8 and 9, consider the block diagram in Figure 9.69 where G(s)= 9 (s+1)(s+3s+9) and the controller is the proportional-plus-derivative (PD) controller G(s) = K(1+Tas).