Discrete Math: Proving a Homework Statement

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Discussion Overview

The discussion revolves around a discrete mathematics homework problem involving limits and proofs. Participants explore various approaches to proving a statement related to limits, particularly focusing on the behavior of the function as it approaches infinity.

Discussion Character

  • Homework-related
  • Exploratory
  • Mathematical reasoning

Main Points Raised

  • One participant expresses uncertainty about the problem and suggests that they arrived at a number by working backwards, questioning the validity of assuming the conclusion is true for a proof.
  • Another participant introduces the limit of a sequence defined as \( a_n = 2^{1/n} \) and suggests using the definition of limits with an epsilon approach.
  • A different participant indicates confusion regarding the epsilon definition of limits.
  • One participant questions whether the others are familiar with the definition of limits, implying it may be necessary for the discussion.
  • Another participant suggests considering negative integers for \( n \) in the context of the problem.
  • One participant shares their experience of graphing the function and concludes that \( r > 0.5 \), but expresses uncertainty about how to prove this mathematically, noting that graphing is not favored by their professor.
  • A later reply proposes solving the equation \( 2^{1/x} = r \) first and using graphing as a source of inspiration for finding an integer \( n \) that satisfies the inequality.

Areas of Agreement / Disagreement

Participants do not appear to reach a consensus, as there are multiple competing views on how to approach the proof and varying levels of understanding regarding the definition of limits.

Contextual Notes

Some participants express uncertainty about the definitions and concepts involved, particularly the epsilon-delta definition of limits, which may affect their ability to engage with the problem fully.

planauts
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Homework Statement


http://puu.sh/1OfE2

Homework Equations


The Attempt at a Solution


I am not really sure about this one! :(
I think it's 1 because
http://puu.sh/1OfY0
http://puu.sh/1OfYE

I came up the number by working backwards (assuming the conclusion is true). However, for a proof, I cannot assume the conclusion is true and try proving the hypothesis. Could someone nudge me to the right direction in proving this statement?

Thanks!
 
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As you say,
\lim_{x \to \infty} 2^{\frac{1}{x}} = 1
But since this is discrete mathematics, perhaps it's more intuitive to define an = 21/n and write
\lim_{n \to \infty} a_n = 1

Now can you solve it if I say: "r = 1 + \epsilon" and "definition of limit"?
 
No, I don't understand the second part with epsilon.
 
Do you know what the definition of the limit is?
 
Consider n<0
 
When I graphed it, i found out that r > 0.5 because 2^(-1) is 0.5 since n has to be int and -1 is an int but i don't know how to prove it. Graphing is not a good way, according to my Prof.
 
If you haven't learned the definition of limit yet, another approach is as follows: try solving the equation 2^(1/x) = r first. Once you find x for which the equality holds, you can may use your graph for inspiration for an integer n such that the inequality holds.
 

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