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Homework Help: Analysis: No strictly increasing fn such that f(Q)=R

  1. Oct 14, 2011 #1
    1. The problem statement, all variables and given/known data
    Prove that there is no strictly increasing function f: Q->R such that f(Q)=R. (Do not use a simple cardinality argument)

    2. Relevant equations
    The section involves montone functions, continuity and inverses. I believe the theorem to be used is that a monotone function on an interval has a continuous inverse, and the intermediate value theorem.

    3. The attempt at a solution
    In class, our professor said that f has a continuous inverse, but I'm not sure why exactly. From there, I realize you can use the intermediate value theorem to contradict the fact the inverse is continuous, by letting c belong to the irrationals and showing it is not in the image.

    EDIT: I now have everything down to proving that a strictly increasing, onto function f:Q->R is continuous
    Last edited: Oct 14, 2011
  2. jcsd
  3. Oct 15, 2011 #2
    Meant to say I have it down to proving that a strictly increasing, onto function: f: R->Q is continuous
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