21 P. 4. Given a unity positive feedback system with open-loop transfer function G(s) = - s^5 + s^4 + 7s^3 + 7s^2 + 21s. Using the Routh table, determine how many poles are in the right half-plane, in the left half-plane, and on the jω-axis.
R(s)
C(s)
K
s(s+7)(s+3)
R(s)
E(s)
C(s)
G(s)
P.5. For the system shown above, find the value of gain K that will make the system oscillate (marginally stable). Also, find the frequency of oscillation.