Limit Comparison Theorem: Proving the Relationship Between Two Functions

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Homework Help Overview

The discussion revolves around proving a relationship between two functions using the Limit Comparison Theorem, specifically addressing the implication that if f(x) is less than or equal to g(x), then the limit of f(x) should be less than or equal to the limit of g(x).

Discussion Character

  • Exploratory, Conceptual clarification, Assumption checking

Approaches and Questions Raised

  • The original poster attempts to use the definition of limits but expresses difficulty in progressing. Some participants question whether the limit of a function can exceed its range, while others suggest a proof by contradiction to explore the implications of the limits.

Discussion Status

The discussion is active, with participants exploring different angles on the problem. Some guidance has been offered regarding proof techniques, and there is an ongoing examination of the assumptions related to the limits and their values.

Contextual Notes

There is a noted confusion regarding the relationship between limits and the range of function values, which remains unresolved in the discussion.

cristina89
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Homework Statement


Prove that if f(x)<=g(x) then lim f(x) <= lim g(x).

Homework Equations


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The Attempt at a Solution



I've tried by definition of limit, but I didn't get anywhere with this... Can anyone help me??
 
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Does the limit of a function ever give you a value that is higher than the range of values of the function itself?
 
Try a "proof by contradiction". Suppose lim f(x)> lim g(x). Let \alpha= lim f(x)- lim g(x) and choose \epsilon= \alpha/2.

I am puzzled by phind's question. The answer is "yes, it does" but I don't see how that helps here.

(Note, by the way, if the condition were "f(x)< g(x)" then it would NOT be true that "lim f(x)< lim g(x)". Phind's suggestion would be helpful in proving that.)
 
HallsofIvy said:
I am puzzled by phind's question. The answer is "yes, it does" but I don't see how that helps here.

QUOTE]

Hm ... I guess I'm missing something. I don't see how the limit of a function could possibly give you a value that is outside the range of the possible values of the function.
 
Hm ... I guess I'm missing something. I don't see how the limit of a function could possibly give you a value that is outside the range of the possible values of the function.

Try ##\lim_{x\to\infty}\frac 1 x##.
 
Last edited:
LCKurtz said:
Try ##\lim_{x\to\infty}\frac 1 x##.

OK, thanks. I got it.
 

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