# Homework Help: Question about system stability

1. Apr 15, 2014

### Drao92

If a system transfer function has a pole equal with 1 , j, cos(pi/4)+j*sin(pi/4) in other words its location is on the margin of the unit circle, its the system stable? In my opinion its not stable because we have a sum of 1 which doesnt converge but im not sure. Everywhere ive read it says the poles must be inside the unit circle but it doesnt say anything about poles on the margin of the unit circle. Can somebody give me a precise answer? Thanks!
Edit: Im referring to z-plane

2. Apr 15, 2014

### Staff: Mentor

What does this (above) mean?
What's the z-plane? Do you mean the plane z = 0?

3. Apr 16, 2014

### Drao92

Iam talking about z transform and stability analysis.
Like if H(z)=z/(z-1), pole is 1. is it stable?
I have exam in 5 hours and i need an answer .

Last edited: Apr 16, 2014
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