Consider the following open-loop transfer function:
\(G = \frac{{K\left( {s + 2} \right)}}{{\left( {s + 1} \right)\left( {s + 4} \right)}}\)
The characteristic equation of the unity negative feedback will be
1
(s + 1)(s + 4) + K (s + 2) = 0
2
(s + 2)(s + 1) + K (s + 4) = 0
3
(s + 1)(s - 2) + K (s + 4) = 0
4
(s + 2)(s + 4) + K (s + 1) = 0