Q&A #19812

Explaining concept -x=2 is equal to x=-2

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From: Gail (for Teacher2Teacher Service)
Date: Oct 25, 2008 at 07:44:33
Subject: Re: Explaining concept -x=2 is equal to x=-2

Hi Sam, 

Has your class talked about coefficients?  I think the key here is that -x
really has a coefficient of -1.  So, if you want "the x all by itself", you
have to divide both sides by -1, and you have 

-x = 2
__   __

-1   -1

and that simplifies to 

x = 2/-1, or -2

another way to look at it is using the idea of opposites, which is what I 
teach my students.  that - means "the opposite of", so -x means "the 
opposite of x. If the opposite of x is 2, then x must be -2.

Hope this gives you someplace to start...  :-)   

 -Gail, for the T2T service

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