           ## Coordinate Graphing

Coordinate graphing sounds very dramatic but it is actually just a visual method for showing relationships between numbers. The relationships are shown on a coordinate grid. A coordinate grid has two perpendicular lines, or axes, labeled like number lines. The horizontal axis is called the x-axis. The vertical axis is called the y-axis. The point where the x-axis and y-axis intersect is called the origin. The numbers on a coordinate grid are used to locate points. Each point can be identified by an ordered pair of numbers; that is, a number on the x-axis called an x-coordinate, and a number on the y-axis called a y-coordinate. Ordered pairs are written in parentheses (x-coordinate, y-coordinate). The origin is located at (0,0). Note that there is no space after the comma.

The location of (2,5) is shown on the coordinate grid below. The x-coordinate is 2. The y-coordinate is 5. To locate (2,5), move 2 units to the right on the x-axis and 5 units up on the y-axis. The order in which you write x- and y-coordinates in an ordered pair is very important. The x-coordinate always comes first, followed by the y-coordinate. As you can see in the coordinate grid below, the ordered pairs (3,4) and (4,3) refer to two different points! The function table below shows the x- and y-coordinates for five ordered pairs. You can describe the relationship between the x- and y-coordinates for each of these ordered pairs with this rule: the x-coordinate plus two equals the y-coordinate. You can also describe this relationship with the algebraic equation x + 2 = y.

 x-coordinate x + 2 = y y-coordinate ordered pair 0 0 + 2 = 2 2 (0,2) 1 1 + 2 = 3 3 (1,3) 2 2 + 2 = 4 4 (2,4) 3 3 + 2 = 5 5 (3,5) 4 4 + 2 = 6 6 (4,6)

To graph the equation x + 2 = y , each ordered pair is located on a coordinate grid, then the points are connected. Notice that the graph forms a straight line. The arrows indicate that the line goes on in both directions. The graph for any simple addition, subtraction, multiplication, or division equation forms a straight line. Finding and Graphing Points
for Linear Relationships

Finding the Length of a Line

 Mathematics Center | Math Steps Education Place | Site Index Copyright © 1999 Houghton Mifflin Company. All Rights Reserved. Terms and Conditions of Use | Privacy Policy.