A system with characteristic equation s^4 + 2s^3 + 11s^2 + 18s + 18 = 0 will have closed loop poles such that
- A. All poles lie in the left half of the s-plane
- B. All poles lie in the right half of the s-plane
- C. Two poles lie symmetrically on the imaginary axis of the s-plane.
- D. No pole lies on the imaginary axis of the s-plane.
Answer: C. Two poles lie symmetrically on the imaginary axis of the s-plane.
Explanation: Routh array: s⁴: 1, 11, 18; s³: 2, 18; s²: 2, 18; s¹: row of zeros! Auxiliary polynomial A(s) = 2s² + 18 = 0 gives s = ±j3, so two poles lie symmetrically on the imaginary axis.