Why does this function make it easy to prove continuity with sequences?

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SUMMARY

The discussion focuses on proving the continuity of the function defined as $$f(x)=\begin{cases}{\left |{x}\right |}&\text{if}& x \in \mathbb{Q}\\ 0 & \text{if}& x \not \in \mathbb{Q}\end{cases}$$ at the point zero. Participants emphasize that to show $$\lim_{x\to 0} f(x) = 0$$, one must demonstrate that for any sequence $$\{x_n\}$$ converging to zero, $$f(x_n)$$ also converges to zero. The proof requires using the formal definition of limits and continuity, specifically the epsilon-delta criterion, to establish that $$|f(x_n) - f(0)| < \epsilon$$ for sufficiently large $$n$$.

PREREQUISITES
  • Understanding of limits and continuity in real analysis.
  • Familiarity with piecewise functions and their properties.
  • Knowledge of the epsilon-delta definition of limits.
  • Ability to work with sequences and their convergence.
NEXT STEPS
  • Study the epsilon-delta definition of continuity in detail.
  • Learn how to prove limits using sequences in real analysis.
  • Explore properties of piecewise functions and their continuity.
  • Investigate examples of functions that are continuous at some points and discontinuous at others.
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Students of mathematics, particularly those studying real analysis, educators teaching calculus concepts, and anyone interested in understanding the formal proofs of continuity and limits.

  • #31
I thought the goal was showing continuity using ##[x_n \rightarrow x ]\rightarrow [f(x_n) \rightarrow x] ##
 
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  • #32
FactChecker said:
It's as simple and basic as that.
Furthermore, it's the real thing:wink:
PeroK said:
A simpler approach was simply to note that:
$$|f(x) - f(0)| = |f(x)| \le |x|$$
Definitively, compañero.
WWGD said:
I thought the goal was showing continuity using ##[x_n \rightarrow x ]\rightarrow [f(x_n) \rightarrow x] ##
Yes.
Mark44 said:
This...
This... Was as simple as @PeroK knew; as hard as I turned it.
A thousand thanks, milesker, bihotzez.
HNY, PF!
 
  • #33
mcastillo356 said:
A thousand thanks, milesker, bihotzez.
Are the last two words Basque? I definitely don't recognize them as Spanish.
 
  • #34
J
Mark44 said:
Are the last two words Basque? I definitely don't recognize them as Spanish.
Just basqueing in the glory of Spanish regional languages.
 
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  • #35
In Basque, yes, "a thousand thanks, from the heart".
PD @FactChecker, I feel I should have written a few more about #30, but I've plunged headlong into the next chapter, integration.
Love, greetings, PF.
 
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