The necessary condition of stability are:
(a) Coefficient of characteristic equation must be real and have the same sign
(b) Coefficient of characteristic equation must be non-zero
(c) Both of the mentioned
(d) Coefficient of characteristic equation must be zero
The question was posed to me in an internship interview.
Enquiry is from Necessary Conditions for Stability and Non-Linear Systems in portion Stability and Algebraic Criteria of Control Systems