Proving the Claim for g(x) with continuous function f(x)

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Homework Help Overview

The problem involves a continuous function f defined on the interval [0,1] with the condition that f(0) equals f(1). The task is to prove the existence of a number x such that f(x) equals f(x + 1/n) for any natural number n.

Discussion Character

  • Exploratory, Conceptual clarification, Mathematical reasoning

Approaches and Questions Raised

  • The original poster attempts to analyze the function g(x) = f(x) - f(x + 1/n) but expresses uncertainty about the usefulness of this approach. They note observations about repeating terms for different values of n. Some participants question the choice of n and emphasize the need to show the result holds for any n. Others suggest using the intermediate value theorem based on the behavior of g at specific points.

Discussion Status

The discussion is ongoing, with participants exploring various interpretations of the problem. Some guidance has been offered regarding the application of the intermediate value theorem, and there is a suggestion to consider the sum of g at specific intervals. However, no consensus has been reached on the next steps or the validity of the claims made.

Contextual Notes

Participants are navigating the constraints of the problem, particularly the requirement to demonstrate the result for any natural number n, which has led to questions about the implications of specific values of x and n.

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Homework Statement


Suppose f is continuous on [0,1] and f(0)=f(1). Let n be a natural number. Prove that there is some number x, such that f(x)=f(x+1/n).


Homework Equations


The hints says to consider g(x)=f(x)-f(x+1/n)

The Attempt at a Solution


I've tried to consider the function g(x), but I haven't gotten anything useful from it. When I've tried various values of n, like 1/2, 1/3...I've noticed that there are repeating terms and I can manipulate the terms a bit to get like g(0)=-g(1/2) for n=1/2 and the like, but I am not sure where to go with this
 
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What's wrong with x =0 and n=1?
 
dirk_mec1 said:
What's wrong with x =0 and n=1?
You don't get to choose ##n##. It is chosen for you. In other words, you have to show there is a solution for ANY ##n##.
 
If ##g(0) = 0## then you can simply take ##x = 0##. If ##g(0) > 0##, then I claim there must be some other point ##x## such that ##g(x) < 0##, and then you can apply the intermediate value theorem. Can you prove this claim? Hint: consider ##g(0) + g(1/n) + \ldots + g((n-1)/n)##.
 

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