ISRO Electronics & Communication (ECE) 2017 - Question 76

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Topic: Control Systems

Characteristic equation of $H(s)$ is given as $3s^4+2s^3+5s^2+s+2=0$ is

  • A. unstable
  • B. stable
  • C. all poles in right half plane
  • D. unstable with only one pole in right half plane

Answer: A. unstable

Explanation: Applying the Routh-Hurwitz criterion to the polynomial $3s^4+2s^3+5s^2+s+2=0$, the first column of the Routh array evaluates to 3, 2, 3.5, -0.443, and 2. Since there are two sign changes (from positive to negative and back to positive), there are two poles in the right half of the s-plane, making the system unstable.

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