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Absolute Value Problem

  1. Dec 16, 2012 #1
    I'm currently reviewing pre-calculus material and encountered a little problem with an absolute value expression.

    |3-x|=x-3

    Now the way I learned absolute value expressions was that there's a positive and a negative case. So I got:

    3-x=x-3 x=3 and -(3-x)=x-3 gives 0=0. Stupid question, but isn't 0=0 in general valid for all values of x? And I don't understand how you get to the solution x≥3.
     
  2. jcsd
  3. Dec 16, 2012 #2

    mfb

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    Staff: Mentor

    If you distinguish two different cases, you should keep in mind where those cases apply. Here, your case ##3-x \leq 0## is valid for ##x \geq 3## only.
     
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