13. Consider a unity negative feedback system with a loop transfer function (with nominal values)

K L(s) = Ge(s)G(s)= 4.5 s(s+a)(s+b) s(s+1)(s+2) Using the Routh-Hurwitz stability analysis, it can be shown that the closed-loop system is nominally stable. However, if the system has uncertain coefficients such that 0.25 a2, 1