P9.4 The Nyquist plot of a conditionally stable system is shown in Figure P9.4 for a specific gain K.

(a) Determine whether the system is stable, and find the number of roots (if any) in the right-hand s-plane. The system has no poles of G s c( )G s( ) in the right half-plane.

(b) Determine whether the system is stable if the −1 point lies at the dot on the axis.

jv G(jw)G(jw)-plane 0 FIGURE P9.4 Nyquist plot of conditionally stable system.