• Similarly, if the LTI system is anti-causal , then



In this case, the ROC of is a region in the given by

• The contour is called the unit circle. Thus represents evaluated on the unit circle.
• can be expressed as the ratio of two polynomials in
  

       The polynomials and helps us in analyzing the properties of a linear system in terms of the zeros and poles of defined by -

       Zero - the point in the where Consequently at such a point.

       Pole - the point in the where Consequently at such a point. The ROC of does not contain any pole. The poles and zeroes and unit circle on the complex plane are illustrated in Figure 2.