Algebra 1 X Y Coordinate Mapping
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The Big Picture
X Y Coordinate Mapping

 
 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

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