# Stability Theory – 6

6. The characteristic equation 1 + G(s) R(s) = 0 of a system is given by

$s^4 + 6s^3 + 11s^2 + 6s + K = 0$

For the system to remain stable, the value of gain K should be :

(a)  zero
(b)  greater than zero but less than 10
(c)  greater than 10 but less than 20
(d)  greater than 20 but less than 30