Is Every Convergent Sequence in a Closed Set a Cauchy Sequence?

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SUMMARY

The discussion centers on the relationship between closed sets and Cauchy sequences in the context of real analysis. It establishes that a set F is closed if every Cauchy sequence contained in F converges to a limit that is also within F. The participants explore the formal proof, emphasizing that closed sets contain all their limit points and discussing the properties of Cauchy sequences, specifically how they relate to convergence. The conclusion drawn is that every convergent sequence in a closed set is indeed a Cauchy sequence.

PREREQUISITES
  • Understanding of Cauchy sequences and their properties
  • Knowledge of closed sets in real analysis
  • Familiarity with the triangle inequality in metric spaces
  • Basic concepts of limits and convergence in sequences
NEXT STEPS
  • Study the formal proof of the relationship between closed sets and Cauchy sequences
  • Explore the properties of limits in metric spaces
  • Learn about the implications of the triangle inequality in analysis
  • Investigate examples of closed sets in different metric spaces
USEFUL FOR

Students of real analysis, mathematicians focusing on topology, and anyone studying the properties of sequences and convergence in closed sets.

kathrynag
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Homework Statement



A set F\subseteqR is closed iff every Cauchy sequence contained in F has a limit that is also an element of F.

Homework Equations





The Attempt at a Solution


Let F be closed. Then F contains its limit points.
This means x=lima_{n} are elements of F.
 
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I guess the formal proof is getting me:
Every closed set contains all of its limit points. Then there is a a neighborhood(x) such that the intersection of F is not equal to {x}. I guess I don't see how to get to the Cauchy sequence from there.

Other direction: Let an be cauchy sequence such that an has a limit contained in F.
an is a Cauchy sequence if abs value(an-am)<epsilon
A limit exists for an if abs value(an-a)<epsilon
we can rewrite an-am as (an-a)+(a-am)
Then by the triangle inequality, abs value(an-am)<abs value(an-a)+abs value(a-am)
I'm stuck going from there to the set being closed
 
i think every convergent sequence in F is a cauchy sequence.
 

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