Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Homework Help: Smallest positive irrational number

  1. Apr 30, 2010 #1
    1. The problem statement, all variables and given/known data

    Prove that there is no smallest positive irrational number

    2. Relevant equations



    3. The attempt at a solution

    I have no idea how to do this, please help walk me through it.
     
  2. jcsd
  3. Apr 30, 2010 #2

    Mark44

    Staff: Mentor

    Do you know how to do a proof by contradiction? If so, assume that there is a smallest positive irrational number, and then produce another one that's even smaller.
     
  4. Apr 30, 2010 #3
    I thought the way to do it was by contradiction. But I'm confused as to how to produce a generalized irrational number, and then like you say, get one smaller than that.
     
  5. May 1, 2010 #4
    Label your arbitrary irrational number a. Starting with a, can you think of a way to get a number smaller than a? There may be many ways to do this. Once you have a candidate idea in mind, try to prove that the number you get is always irrational.
     
  6. May 1, 2010 #5
    You could try using the density of rationals in R
     
  7. May 1, 2010 #6

    HallsofIvy

    User Avatar
    Science Advisor

    If r is a positive irrational number, then r/2 is a smaller positive irrational number.
     
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook