Figure 1 below shows a typical control system block diagram. R(s) is the reference input, D(s) D(8) R(s) E(s) U(s) Y(s) K C(s) G(s) Figure 1: Feedback system for Problem 6. is the disturbance input, Y(s) is the output. G(s) and C(s) are respectively is the plant and controller transfer functions, with 50 G(s) = s (s2+15s+50) Assume first that a proportional controller is utilized (C(s) = 1). Determine the value of K at the stability limit and find the frequency of oscillation at the stability limit.