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100x - x

  • Thread starter thomas49th
  • Start date
  • #1
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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
 

Answers and Replies

  • #2
486
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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.
 
  • #3
arildno
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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.
 
  • #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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