: set of rational numbers, which are of the form. : set of real numbers represented by a finite or infinite decimal expansion. There(cid:495)s no standard notation for the set of complex numbers (which are of the form. All numbers are either complex or real, and the real group can be broken down into those sets above. We can visualise the set of real numbers as a number line: The real numbers are ordered (from left to right in the visualisation above). Given any two real numbers must be either greater than, less than, or exactly equal to and. An interval is a set of real numbers. Endpoints are not possible values of which is some point in the interval. Thus the endpoints are not in the interval. represents. Endpoints are possible values of which is some point in the interval.