We know from an earlier post that a number shows where you are on a number line. For example, we know the number 7 tells we are 7 units to the right of 0. The number -9 tells us we’re nine units to the left of zero.
What happens if we need to locate a point against two number lines, though. Let’s call our normal number line the “x-axis”. Then, let’s create another number line that intersects the x-axis at zero on both lines, and call this new vertical number line the “y-axis”.
Now we need to describe a point in relation to both axes. Let’s start with that point 7 units away from 0 on the x-axis. That point could be on the x-axis, or it could be somewhere above or below the line. That’s where the y-axis comes in. It tells us how many units above or below the x-axis the point is. For example, our point could be located 3 units below the x-axis, making its location on the y-axis -3.
So our point is at 7 on the x-axis and -3 on the y-axis. That’s a lot of words to describe where this point is located, so we can use a shorter notation called the ordered pair.
The basic pattern for an ordered pair is (x, y).
Since we know our values for both axes, we can plug the 7 in for x and the -3 in for y to come up with the ordered pair (7, -3)
The important thing to remember with an ordered pair is that the first number always describes where you are in relation to the x-axis, and the second describes where you are in relation to the y-axis.
