Consider the feedback control system shown in figure.
(a) Find the transfer function of the system and its characteristic equation.

(b) Use the Routh-Hurwitz criterion to determine the range of 'K' for which the system is stable.

Given the $$G\left(s\right)H\left(s\right)=\frac K{s\left(s+1\right)\left(s+3\right)}$$, the point of intersection of the asymptotes of the root loci with the real axis is

The Nyquist plot for the open-loop transfer function G(s) of a unity negative feedback system is shown in figure. if G(s) has no pole in the right half of s-plane, the number of roots of the system characteristic equation in the right half of s-plane is

The open-loop DC gain of a unity negative feedback system with closed-loop transfer function $${{s + 4} \over {{s^2} + 7s + 13}}$$ is