Determine whether each of the following characteristic equations represent a stable or unstable system.

a/ s3 + 6s2 + 11s + 6 = 0

b/ s3 + s2 - 8s - 12 = 0

any ideas guys??

Thanks

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- May 7th 2009, 12:30 PMconners84characteristic equation and stability
Determine whether each of the following characteristic equations represent a stable or unstable system.

a/ s3 + 6s2 + 11s + 6 = 0

b/ s3 + s2 - 8s - 12 = 0

any ideas guys??

Thanks - May 8th 2009, 11:09 PMCaptainBlack
The question is asking is these cubics have one or more of roots with real part greater than 0.

For the first s=-1 is an obvious root, so you can factorise and use the quadratic formula to find the remaining roots.

For the second Descartes rule of signs tell you that the cubic has exactly one positive root.

CB