Determine the range of K that keeps the system stable

[alagez]

Homework Statement

i meet problem below in control system :

G(s)= K(s+4)/s(s+1)(s+2) its a unity feedback system.

1. determine the range of K that keeps the system stable.
2. determine the range of K that makes the system oscillate
3. calculate the frequency of oscillation when the system oscillate

Homework Equations

characteristic equation for stability Routh Hurwitz Creation

The Attempt at a Solution

i have solved the first by determine the range of K by using Routh Hurwitz Table. But, i m very confused when it comes to find the range of K that makes system oscillate. even, i don't understand the term for oscillate. conclusion number 2 and 3 is very confusing.

 

[rude man]

Is G(s) the forward gain with unity feedback? Good idea is to draw us a block diagram.