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Homework Help: What does this mean? modulus

  1. Oct 24, 2012 #1
    udhlG.png

    I thought |r| means the positive values of r? Why do they say it means -1<r<1? Also, if |r| means -1<r<1 then why do they say |r|<1 when |r| is already -1<r<1 ?
     
  2. jcsd
  3. Oct 24, 2012 #2

    Mark44

    Staff: Mentor

    No that's not what |r| means. It means all of the values of r that are within 1 unit of 0. That would include -.5, for example, not just positive values (and zero) of r.
    These two statements say exactly the same thing: |r| < 1 and -1 < r < 1. They are equivalent statements.
     
  4. Oct 24, 2012 #3
    |r| is it not the absolute value of r? if so then I don't understand how it can be negative.

    how can they also be equivalent when they said |r| is -1<r<1 then they are saying |r|<1, which is -1<r<1 < 1?
     
  5. Oct 24, 2012 #4

    Mark44

    Staff: Mentor

    Yes
    Who is "it"? There are two things we're talking about here - r and |r|. Which one do you mean?
    No. I didn't say "|r| is -1<r<1".

    I said that |r| < 1 (first statement) and -1 < r < 1 (second statement) were two statements that said exactly the same thing. They are equivalent statements.
    Now, who are "they"? I said that |r|<1 and -1<r<1 [STRIKE]< 1[/STRIKE] were equivalent statements
     
  6. Oct 24, 2012 #5

    Erland

    User Avatar
    Science Advisor

    There is a typo in the hint. It should be: |r|<1 means -1<r<1.
     
  7. Oct 24, 2012 #6

    Mark44

    Staff: Mentor

    To be honest, I didn't notice that. I have my browser open to less than full-screen width, and didn't notice that hint way off to the right.
     
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