I was wondering what would you classify the damping state (under damped, over-damped, critically damped) a second-order ode system with a negative damping ratio? To me it doesn't make much sense since a negative damping ratio results in an unstable system.
The system I have is:
$G(s) = \frac{5}{s^2-6s+16}$
So solving for the natural frequency and damping ratio:
$\omega_n = \sqrt{16} = 4$
$2 \zeta \omega_n = -6$
$\zeta = \frac{-6}{2 \omega_n} = -0.75$