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Real Numbers

  1. Mar 23, 2010 #1
    If we were to take any two integers on a real number line and mark a point (a number) halfway between the two, do the same in the range between the halfway point and each of the two numbers, and continue the process, would we be able to define all real numbers between the two integers (including irrational numbers) as the limit of a rational expression or a series of rational expressions?
    Last edited: Mar 23, 2010
  2. jcsd
  3. Mar 23, 2010 #2
    I think not. Because whatever you define would not be countable.
  4. Mar 23, 2010 #3


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    Consider in between 0 and 1. You'll end up getting every rational number that has a 2^k in the denominator. These points are dense, so every number between 0 and 1 is a limit of a sequence of them. Then given any two integers a and b, the map f(t)=a(1-t)+bt is a bijection between the intervals [0,1] and [a,b] that preserves your construction (so 1/2 is mapped to halfway between a and b, 1/4 is mapped to one quarter of the way between a and b) and so your construction is dense on any interval between two integers
  5. Mar 24, 2010 #4
    I think the answer is no because the halfway point between any two rational numbers is another rational number. You can't obtain irrational numbers using this method.
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