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(c) The open loop transfer function of a unity feedback system is given by 350 (-0.2) G(s) = (s - 4)(s + d)(s2 - 4s +5)(s2 + 25 - 3) where the constant d is a real number. ) Find all the poles of the open loop transfer function (). (c) The Nyquist diagrams of G(s) for d = 0.75 and d = 2 are given in Figures 3.2 and 3.3, respectively. For each case, using the Nyquist stability criterion, determine the number of poles of the closed-loop system in the right-half plane. Hence, determine the stability of the closed-loop system when d = 0.75 and d = 2, respectively. [8 marks] Nyquist diagram for d-0.75 Imaginary Axis -1.5 -0.5 Real Axis Figure 3.2 Nyquist diagram for d-2 0.5 Imaginary Axis 0 -1.6 -1.4 -1.2 -1 -0.2 0 -0.8 -0.6 -0.4 Real Axis Figure 3.3