Find Limit of x Approaching 4 - Problem Solved

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Discussion Overview

The discussion revolves around the limit of the expression \( \lim_{x \to 4} (3x + \sqrt{x - 4}) \). Participants explore whether the limit exists and the implications of one-sided versus two-sided limits, particularly in the context of real variables.

Discussion Character

  • Debate/contested
  • Mathematical reasoning

Main Points Raised

  • One participant expresses concern about the square root in the limit expression and questions whether a one-sided limit should be considered.
  • Another participant suggests that if not specified, a two-sided limit is understood.
  • It is noted that the limit is typically defined by evaluating limits from both sides, and if they are equal, that is the limit; otherwise, it does not exist.
  • Some participants clarify that if the function does not exist on one side, the one-sided limit can be considered the limit.
  • A later reply emphasizes the importance of adhering to definitions when working over the reals, suggesting that the limit does not exist in this case.
  • There is a suggestion to consult the professor for clarification on how to approach the problem, with a recommendation to state both the limit and the one-sided limit if applicable.

Areas of Agreement / Disagreement

Participants do not reach a consensus on whether the limit exists, with some arguing it does not exist while others suggest it can be interpreted differently based on context.

Contextual Notes

There are unresolved assumptions regarding the definitions of limits and the behavior of the function near the point of interest, particularly concerning the square root term.

Strelka
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I have a question about the limit problem. I need find limit if it exists.

lim x (approach to 4) (3x+square root x-4).
If I plug number for x=4, I get 12. But I am concern about square root. Do I need find one-sided limit from x approach to 4+ and x approach to 4-. Or 12 will be the correct answer?
Thanks, everyone
 
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If it's not specified,then the superior limit is understood.

Daniel.
 
Usually the limit (in the case of real variables) is defined by getting limits on both sides. If they are equal, that is the limit. If not, the limit does not exist.
 
Except when it is clear that the function itself does not exist on one side. Then the one sided limit is the limit.
 
We both assumed the limit & the function were defined on the reals (real intervals).

Daniel.
 
Limit Laminant...


[tex]\boxed{\lim_{x \rightarrow 4} 3x + \sqrt{x - 4} = 12}[/tex]

[/color]
 
You should ask your professor how he would like you to answer. However, I think you should take the strict interpretation -- it's written as a two-sided limit, so don't assume it's a one-sided limit.

When writing your answer, you can always say the limit doesn't exist, and then write down what the one-sided limit is.


P.S. dex: I know everyone knows what you meant, but "limit superior" (written "lim sup") means something else.
 
Yes, I would use the definition. By the definition, if you're working over the reals, the limit doesn't exist. As Hurkyl said, putting down the one-sided limit as well couldn't hurt. But unless it has been clearly stated in class that you have a different definition for limits when the function doesn't exist on one side, then you shouldn't assume so.
 
Thanks guys a lot
 

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