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Lesson 129: The Coordinate Plane
In this quick and easy lesson, we'll learn a bit more about the coordinate plane
We've worked with coordinates in previous lessons, but only ones where the x and y values were positive. Now we're at the point where we'll need to work with negative x and y values. Let's take a look at a full coordinate plane. Here you can see that our plane (flat surface) has been divided into four quadrants. Notice that the horizontal dividing line is called the x-axis, and the vertical dividing line is called the y-axis. This is always how we set up a coordinate plane for graphing and plotting points. This should be memorized.
As
we move to the right on the x-axis, our values increase.
Values to the right of the y-axis are positive, and those to the
left are negative. As we move up on the y-axis, our values
increase. Values above the x-axis are positive, and those
below are negative. Practice recreating this coordinate plane
on graph paper until you can do so easily. Be sure to label
the axes. In many cases, you will lose points on a test if you
do not.
The point where the axes intersect is called the origin. It has coordinates (0, 0). When we list the coordinates of a point, we always list the x coordinate first, then the y-coordinate. We've seen the basics of this before. This is known as the Cartesian coordinate system.
To determine the coordinates of any point that you plot on the graph, first see how far to the left or right it is. That is your x-coordinate. Then see how far up or down it is, and that is your y-coordinate.
Notice that each quadrant has a Roman numeral associated with it. Quadrant I, usually abbreviated QI, has positive values of x and y. QII has negative x values, but positive y. QIII has negative x and negative y. QIV has positive x, and negative y.
You'll have more practice working with the Cartesian coordinate system in later lessons. Make sure that you have some graph paper on hand so that you can practice with graphing. It is a very big topic in math.
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