The real numbers can be represented geometrically by a coordinate axis called a real number line. The number associated with a particular point on a real number line is called the coordinate of the point. It is customary to label those points whose coordinates are integers. The point corresponding to zero is called the origin, denoted by `0`. Numbers to the right of the origin are positive real numbers; numbers to the left of the origin are negative real numbers.

A real number line provides a picture of the real numbers. That is, each real number corresponds to one and only one point on a real number line, and each point on a real number line corresponds to one and only one real number. This type of correspondence is referred to as a one-to-one correspondence.

Certain order relationships exist between real numbers. For example, if `a` and `b` are real numbers, then
`a` equals `b` (denoted by `a=b`) if `a-b=0`.
`a` is greater than `b` (denoted by `a > b`) if `a-b` is positive.
`a` is less than `b` (denoted by `a < b`) if `a-b` is negative.

On a horizontal number line, the notation

`a=b`	implies that the point with coordinate `a` is the same point as the point with coordinate `b`.
`a > b`	implies that the point with coordinate `a` is to the right of the point with coordinate `b`.
`a < b`	implies that the point with coordinate `a` is to the left of the point with coordinate `b`.

The inequality symbols ` < ` and ` > ` are sometimes combined with the equality symbol in the following manner:

`a >= b`	This is read "`a` is greater than or equal to `b`," which means `a > b` or `a = b`.
`a <= b`	This is read "`a` is less than or equal to `b`," which means `a < b` or `a = b`.

Inequalities can be used to represent subsets of real numbers. For example, the inequality `x > 2` represents all real numbers greater than `2`. A parenthesis at `2` means that `2` is not part of the graph.

The inequality `x <= 1` represents all real numbers less than or equal to `1`. A bracket at `1` means that `1` is part of the graph.