(a) Find a suitable contour Γs in the s-plane that can be used to determine whether all roots of the characteristic equation have damping ratios greater than ζ1,
(b) Find a suitable contour Γs in the .v-plane that can be used to determine whether all the roots of the characteristic equation have real parts less than s = -σ1.
(c) Using the contour of part (b) and Cauchy's theorem, determine whether the following characteristic equation has roots with real parts less than s = -1:
