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Q&A #1530

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

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From: Loyd <Loydlin#aol.com>
To: Teacher2Teacher Public Discussion
Date: 2003030308:55:33
Subject: Re: x squared minus one divided by one minus x

On 2003030123:23:15, Anonymous wrote:
>	
>How do I do this?
>so far I've got (x+1)(x-1)/-(x-1)
>cancel out the x-1
>leaving me with x+2/-1
>the answer is -(x+1) but why why why???
>


Replace "leaving me with x+2/-1" to x+1/-1  
The last expression is equal to -(x+1).

A fraction has three signs:
 +a
+---   You can change any two of them and the fraction will still be
 +b
equavilent to the original.  

Thus:
(x+1)/-1 can be rewritten as:

+ (x-1)
+ -----  which is equal to 
   -1
 -(x-1)
+ -----  which is equal to 
   +1

-(x-1)




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