Question

For what values of K does the polynomial s^4+8s^3+24s^2+32s+K=0 have roots with zero real parts?

(a) 10

(b) 20

(c) 40

(d) 80

I have been asked this question in an internship interview.

My enquiry is from Compensation Techniques topic in section Digital Control Systems of Control Systems

Answer 1

Right answer is (d) 80

For explanation I would say: The solution is obtained by using the Routh-Hurwitz table and in which with the conventional method the number of sign changes are seen in the first row of the table and number of sign changes is equal to the number of the roots on the right half of s plane.