A two-dimensional coordinate system is defined by a pair of intersecting horizontal and vertical number lines. These number lines are referred to as **axes**.

The point at which the axes intersect coincides with the 0 on each number line.

This point of intersection is referred to as the **origin**.

The location of a point on a coordinate grid is identified by an **ordered pair**.

The values of an ordered pair are referred to as **coordinates**.

The first coordinate indicates how far to move from the origin along the horizontal axis.

The second coordinate indicates how to far to move from the origin along the vertical axis.

For example, the origin is located at the point (0, 0).

Most commonly, a coordinate grid has the axes labeled as *x* (horizontal) and *y* (vertical).

The first coordinate of an *xy*-ordered pair is referred to as the *x*-coordinate.

The second coordinate is referred to as the *y*-coordinate.

Point *R* is located by moving 4 spaces to the right of the origin and 3 spaces up. The *x*-coordinate is 4. The *y*-coordinate is 3.

Point *R* is located at (4, 3).

Sometimes ordered pairs are given in a table.

Each set of input/output values can be plotted as a point where the input value is the

*x*-value and the output value is the

*y*-value.

Plot each point by starting at the origin and moving

*x* spaces to the right and

*y* spaces up.