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100x - x

  1. Feb 17, 2007 #1
    Hi, I recall a thingy when you have somthing like

    x = 0.91919191

    then you go 100x = 91.919191
    100x - x = 91

    When do you use this? It's in conjuction with somthing else... looked in my text book cant find it.

    Thanks
     
  2. jcsd
  3. Feb 17, 2007 #2
    Personally, I use that when I have a repeating, non-terminating decimal that I want to get in fractional form so it looks prettier in an equation.
     
  4. Feb 18, 2007 #3

    arildno

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    Dearly Missed

    Why should you care "when is it used"?
    It is a wrong question; the technique is never "used"; rather, it illustrates how you may rewrite a periodic decimal as a fraction.

    That is, the technique amounts to a constructive PROOF of a certain mathematical proposition:
    namely that any periodic decimal can be written as a fraction between two natural numbers, i.e a periodic decimal is necessarily a rational number.
     
  5. Feb 18, 2007 #4

    Gib Z

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    100x - x=99x=91

    x=91/99

    Thats why its used, to get urself a fraction.
     
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