Hi there

I found one zero by guessing, it is s=-1. (I know, this is very disappointing, but very fast compared with other methods like http://en.wikipedia.org/wiki/Newton%27s_method or http://en.wikipedia.org/wiki/Cubic_f...ano.27s_method)

Using polynomial long division leads to

You should be able to find the other two zeros, -3 and -2

All zeros are < 0, therfor I guess (but I don't know) it represents a stable system.

Cheers

Rapha