Can the Rationals be Contained in Open Intervals with Infinitely Small Width?

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Homework Help Overview

The problem involves proving that the rational numbers, as a subset of the real numbers, can be contained within open intervals whose total width is less than any given positive epsilon. The discussion revolves around concepts of countability and convergence in the context of real analysis.

Discussion Character

  • Exploratory, Conceptual clarification, Mathematical reasoning

Approaches and Questions Raised

  • Participants explore the idea of using open intervals around each rational number, considering the countability of the rationals and how to ensure the total width remains below epsilon. Questions arise about the nature of series and convergence related to this setup.

Discussion Status

The discussion includes attempts to formulate a series that converges to epsilon, with participants sharing potential series expressions. There is an ongoing exploration of different approaches to represent the total width of the intervals.

Contextual Notes

Participants are navigating the constraints of the problem, particularly the requirement that the total width of the intervals must be less than any epsilon greater than zero. The implications of countability and convergence are central to the discussion.

zhang128
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Homework Statement


Prove that the rationals as a subset of the reals can all be contained in open intervals the sum of whose width is less than any \epsilon > 0.


Homework Equations





The Attempt at a Solution

 
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You aren't playing the game here. What do you think about the problem? You can't leave the Attempt at a Solution completely blank.
 
ups, my bad. I was thinking that since rationals are countable, I just need to make the open interval around each rational such that the total sum is less than \epsilon. Then the question turns to prove the sum of a finite series converges to the epsilon??
 
zhang128 said:
ups, my bad. I was thinking that since rationals are countable, I just need to make the open interval around each rational such that the total sum is less than \epsilon. Then the question turns to prove the sum of a finite series converges to the epsilon??

Much better, thanks. Can you write a series that converges to epsilon? If you can write a series that sums to say, 1, you should be able to write a series that converges to epsilon.
 
hmmm, like epsilon/(n^2+n)??
 
zhang128 said:
hmmm, like epsilon/(n^2+n)??

Sure, that works. I would have said sum epsilon*(1/2)^n. But whatever you like.
 

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