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Homework Help: Absolute values

  1. Sep 20, 2005 #1
    Can someone give me a n00b lesson in absolute values, i though i remembered, but i don't.

    I got stuck on a

    [tex]-|-8|[/tex]


    :blushing:
     
  2. jcsd
  3. Sep 20, 2005 #2

    Chi Meson

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    Read this as "negative one times the absolute value of negative eight."

    zat help?
     
  4. Sep 20, 2005 #3

    HallsofIvy

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    What is |-8|?

    What is the negative of that?
     
  5. Sep 20, 2005 #4
    this is integers right?

    so uhm..
    [tex]-1|-8| = 7[/tex] ?
     
  6. Sep 20, 2005 #5

    TD

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    No, the absolute value means that you "make the number positive", if it's negative.

    It can be defined by saying:
    |x| = x if x ≥ 0
    |x| = -x if x < 0

    Which is just a more mathematical way of saying that positives stay positive and negatives become positives.

    A few examples may help:
    |2| = 2
    |-3| = 3
    |0| = 0
    |-5/3| = 5/3

    Now, you can solve yours?
     
  7. Sep 20, 2005 #6
    -|-8|= 8

    right?
     
  8. Sep 20, 2005 #7

    TD

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    What is |-8| ? And then again a -, since it say - (|-8|)
     
  9. Sep 20, 2005 #8
    So the answer is -8
     
  10. Sep 20, 2005 #9

    Chi Meson

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    that's right.
     
  11. Sep 20, 2005 #10
    Thank you ^.^ so can i get a laymens explanation(if that is possible) on how this answer is achieved?
     
    Last edited: Sep 20, 2005
  12. Sep 20, 2005 #11

    EnumaElish

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    -(|-8|) is two functions nested: g(f(-8)) where f(x) = |x| and g(y) = -y. With nested functions you begin to peel the onion from the inside, as it were. So you first figure f(-8) is |-8| which is 8 (why?). Then you substitute this answer for y = f(x), inside g and now you have g(8) = -8. Make sense?
     
  13. Sep 20, 2005 #12

    HallsofIvy

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    Do you see where you went wrong with the first one?
    [tex]-1|-8| = 7[/tex]

    I think you recognized that |-8|= 8 but then you subtracted 1

    -|-8| or -1|-8| does not mean subtract the two numbers- it means multiply!
     
  14. Sep 20, 2005 #13
    thank you.
     
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