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Teachers' Lounge Discussion: Factoring out -1 in algebraic expressions

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From: Teresa

To: Teacher2Teacher Public Discussion
Date: 2003040912:16:57
Subject: Re: x squared minus one divided by one minus x



x^2-1/1-x

Factor the top to (x+1)(x-1), a difference of squares. Next
multiply the bottom by -1 to change the signs. Now we have
(x+1)(x-1)/-1(x-1).  
cancel the (x-1)s. Now we have x+1/-1.
Now flip and multiply. x+1 times -1. 

Because the -1 is on the bottom it is actually 1/-1. When you flip
this to multiply you have the correct answer.
Hope this is helpful.

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