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Plottings Points in the Cartesian Plane (page 2 of 3)

Sections: Introduction to the plane, Plotting points, The four quadrants

When you were reading the map, you went over to D and then down to 12. The Cartesian plane works similarly. However, the "D12" designation was unambiguous, because it was easy to tell which stood for which. Even if the designation had been written as "12-D", you still would have known which box to go to, because the "D" would still have been across the top and the "12" would still have been along the side. But in the Cartesian plane, both axes are labelled with numbers.

For instance, if they gave you the direction "(5, 2)" (pronounced as "the point five two" or just "five two"), where would you look? To understand the meaning of "(5, 2)", you have to know the following rule: The x-coordinate (the number for the x-axis) always comes first. The first number (the first coordinate) is always on the horizontal axis.

(By the way, this is sometimes indicated by referring to points as "(x, y)" or "x-y points", reinforcing that the first coordinate is counted off along the x-axis and the second coordinate is counted off along the y-axis. Some people keep track of this by noting that the letters are used in alphabetical order.)

So, for the point (5, 2), you would start at the "origin", the spot where the axes cross:
...then count over five on the x-axis:
...then count up two parallel to the y-axis:
...and then draw in the dot:

Finding the location of (5, 2) and drawing the dot is called "plotting the point (5, 2)".

When plotting, remember that the first number comes from the horizontal axis and the second number comes from the vertical axis. You always go "so far over" and then "so far up or down". Here are a couple more examples.

• Plot the point (4, –5).

Start at the origin:
...then count over four on the x-axis:
...then count down five on the y-axis:
...and draw the dot:

Note that a negative y-coordinate means that you'll be counting down the y-axis, not up.

• Plot the point (–3, –1).   Copyright © Elizabeth Stapel 2006-2008 All Rights Reserved

Start at the origin:
...then count backwards three units:
...then count down one unit:
...and then draw the dot:

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