| So what we're going to do | |||
| is draw a picture of the equation. | |||
| Maybe you've seen something called a number line. | |||
| It looks like this ... | |||
|
|
|||
| In these equations, we have two letters: X and Y | |||
| To see them both at the same time, | |||
| we're going to use two number lines. | |||
| One that looks like this to record the X values ... | |||
|
|
|||
| and one that looks like this to record the Y values ... | |||
|
|
|||
| We're going to use them both together at the same time. | |||
| Like this ... | |||
|
|
|||
| Now here's the trick. | |||
| When we used a single number line | |||
| we put the dots right on the line. | |||
| When we use an X and a Y number line together, | |||
| we usually don't put the dots right on the lines. | |||
|
Here's what we do ... |
|||
| Let's say we have an equation like ... | |||
|
2X - 3 = Y |
|||
| and we chose X = 2 for our first X value. | |||
| Why did I choose 2? Because I like 2. | |||
|
When YOU do these problems by yourself |
|||
| then you can chose any number that you like! | |||
| 2(2) - 3 = Y | |||
| 4 - 3 = Y | |||
| 1 = Y | |||
| So we have X = 2 and Y = 1. | |||
| To find that point go to X = 2 on the horizontal number line. | |||
| And draw a line up and down (vertically) | |||
| and go to Y = 1 on the vertical number line | |||
| and draw a line from left to right (horizontally). | |||
| Where they cross, is the point where X = 2 and Y = 1. | |||
|
|
|||
| We draw a dot at that point | |||
| and sometimes even write down the X and Y values next to it. | |||
| If we have a lot of points to draw, | |||
| it might take up too much space to write | |||
| X = 2 and Y = 1 or something like that at each point. | |||
| So instead, we just write (2,1). | |||
| The X value is always listed first. | |||
| So we have ... | |||
|
|
|||
| Let's find another point. | |||
| How about when X = 0 ... | |||
| 2(0) - 3 = Y | |||
| 0 - 3 = Y | |||
| -3 = Y | |||
| So where X = 0, Y = -3 | |||
| Find that point on the drawing ... | |||
|
|
|||
| So since X = 0, one of our lines is on the Y number line | |||
| (called the Y axis). | |||
| The point is at Y = -3 on the Y axis. | |||
| The point gets named (0,-3) ... | |||
|
|
|||
| Showing both points together at the same time we have ... | |||
|
|
|||
|
copyright 2005 Bruce Kirkpatrick |
|||
