Help to prove that an interval will lead to positive functions?

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Homework Help Overview

The problem involves proving that for a continuous function f at a point c, where f(c) is greater than zero, there exists an open interval (a,b) around c such that f(x) remains positive for all x within that interval.

Discussion Character

  • Exploratory, Conceptual clarification, Mathematical reasoning

Approaches and Questions Raised

  • Participants discuss using the epsilon/delta definition of continuity and the sign preserving property. There are attempts to clarify how to apply these concepts, with some questioning the reasoning behind specific choices like epsilon.

Discussion Status

The discussion is ongoing, with participants providing hints and references to relevant concepts. Some have expressed confusion about the application of the sign preserving property and the continuity definition, while others have attempted to demonstrate their understanding without reaching a consensus.

Contextual Notes

There are indications of confusion regarding the problem's requirements and the proper forum for posting homework questions. Some participants have noted the need for clear attempts at the problem before seeking help.

mathkillsalot
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Homework Statement



Let f be continuous at c and f(c)>0. Prove that there is an open interval (a,b) centered at c such that f(x)>0 for all x that are elements of (a,b)

Homework Equations



we are supposed to use the sign preserving property??

The Attempt at a Solution



I tried assigning all x as numbers greater than zero but then realized it wouldn't work since the f(x) is the one that has to be greater than 0. But the function isn't given.
Please help me...
 
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Use the epsilon/delta definition of continuity. Pick epsilon=f(c)/2.
 
uhmmmm...can you please demonstrate??
and how did you get your epsilon?
 
i used the definition of sign preserving property to prove that f(a) and f(b) are positive.
just assigned all x that are elements of (a,b) to be greater than 0...
My answer seemed to be correct...
 
but it's not checked yet
 
What is this "sign preserving property" you are talking about?
 
Do you have multiple accounts ? This is not allowed :-(.

The same question and the same mistake was posted by "another" user in the calculus and beyond section.
 
Last edited:
  • #10
no no i don't. I think I did post this question twice though. Didn't see the forum for homework at first.

though if you're talking about goodheavens, that person might be someone from the same school as me
 
  • #11
mathkillsalot said:
no no i don't. I think I did post this question twice though. Didn't see the forum for homework at first.

though if you're talking about goodheavens, that person might be someone from the same school as me

Okay,sorry about the confusion. :-)
 

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