If f(c) = infinity and c is in [a,b]

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Discussion Overview

The discussion revolves around the implications of a function f having a value of infinity at a point c within a closed interval [a,b]. Participants explore the relationship between continuity, boundedness, and the definition of functions in this context.

Discussion Character

  • Debate/contested

Main Points Raised

  • One participant questions whether f(c) = infinity implies that f is not continuous at c, suggesting that infinity is undefined.
  • Another participant asserts that if f(c) = infinity, then f is not continuous.
  • A participant proposes that if a function is continuous on a finite interval [a,b], it must be bounded.
  • One response supports this by stating that there exists a superior bound N such that f(x) ≤ N for every x in [a,b], and similarly for an inferior bound.
  • A clarification is made that continuity on a closed and bounded interval implies boundedness, emphasizing the closed nature of the interval [a,b].
  • A later reply challenges the notion of f being a function if it takes the value of infinity at c, arguing that f would not be defined at that point.
  • Another participant humorously claims to have invented the mean value theorem, though this statement appears unrelated to the main discussion.

Areas of Agreement / Disagreement

Participants express differing views on the implications of f(c) = infinity, particularly regarding continuity and the definition of functions. There is no consensus on these points.

Contextual Notes

Some assumptions about the nature of functions and continuity are not explicitly stated, and the discussion does not resolve the implications of infinity in this context.

rsnd
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if f(c) = infinity and c is in [a,b]
is it equivalent to saying
f is not cont. at c ? because infinity is undefined?


Thanks
k.cv
 
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It's NOT continuous.
 
SO it would also imply that if a function is cont. in a finite interval [a,b] then its bounded?
 
Yes, it has superior bound. There exist a number N such that f(x)<= N for every x in [a,b]. Geometricly speaking this means there exist a parallel line to the horizontal axis. And of course a inferior bound, the same for a number N such that f(x) >= N for every x in [a,b].
 
Last edited:
If a function f is continuous on a closed and bounded interval, then it is bounded. You implied "closed" when you said [a,b] but I want to make sure that is clear.
 
Last edited by a moderator:
rsnd said:
if f(c) = infinity and c is in [a,b]
is it equivalent to saying
f is not cont. at c ? because infinity is undefined?


Thanks
k.cv


If you're claiming f is a function from [a,b] to R, then f is not defined at c, and actually f therefore isn't a function, never mind a continuous one.
 
nice...I just invented the mean value theorom!
 

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