Algebra 1 Dependent Variables
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Another Question Mark
Dependent Variables

 
 When we started working with X's we had problems like this ...
 

 3X - 5 = 0

 
 Then we solved for X.
 
 Now, we are going to look at ...
 

 3X - 5 = ?

 
 Instead of a zero, we've got a question mark on the right side.
 Here the game is, feed in a number for X
 and see what the ? turns out to be.
 If X = 2, then ...
 3(2) - 5 = ?
 6 - 5 = ?
 1 = ?
 
 So when X = 2, the question mark equals 1.
 
 If X = -7, then ...
 3(-7) - 5 = ?
 -21 - 5 = ?
 -26 = ?
 
 We can chose anything that we want for X
 and then figure out what the question mark is.
 
 Before when we had a question mark in the problems,
 math people said:

"Yuk, we can't have a question mark in an equation."

 "that looks terrible!"
 "Use an "X" instead"
 
 Guess what,
 math types still don't like question marks in equations.
 
 X is already busy, so they got the next best thing.
 So what's next to X ?
 

 Y

 
 So instead of writing ...

 3X - 5 = ?

 
 We write ...

 3X - 5 = Y

 
 But it means the same thing!
 
 So now when we choose 2 as the value of X (X = 2),
 we get ...
 3(2) - 5 = Y
 6 - 5 = Y
 1 = Y
 
 When we choose -7 for X (X = -7)
 we get ...
 3(-7) - 5 = Y
 -21 - 5 = Y
 -26 = Y
 
 OK, I know it's not a big change,
 but sometimes math people are easily amused.
 
 We could be here until the end of time
 choosing values for X and seeing what we get for Y,
 but life's too short.
 We need a new way to look at this kind of equation.
 
 Maybe we could just have something that we could look at,
 and know that if X was this then Y was that
 without having to do the math for each and every number.
 We need to be able to see the BIG PICTURE.
 
 POP QUIZ
 Guess what's on the next page?
 

   copyright 2005 Bruce Kirkpatrick

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