Q1: If Nyquist plot has a encirclement of (-1 + jo) point, the system is stable if

ANS:A - there are no poles of G(s) H(s) in right-half plane

In Nyquis plot N=Z-P, N=no.of encirclements about origin, P=poles, Z=zeros, i.e.,if P=0 in order to get the system stable, therefore there will be no poles in the RHS plane.

N = 0 (no encirclement), so Z = P = 0 and Z = P.
If N = 0, P must be zero therefore system is stable.