3. If the outmost pole(s) is (are) first-order pole(s) of the z-transfer function HðzÞ and on the unit circle on the z-plane pole-zero plot, then the system is marginally stable.
4. If the outmost pole(s) is (are) multiple-order pole(s) of the z-transfer function HðzÞ and on the unit circle on the z-plane pole-zero plot, then the system is unstable.
5. The zeros do not affect the system stability