What is the limit of a^x when a tend to infinity and x tend to 0?

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    Infinity Limit
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Discussion Overview

The discussion centers on the limit of the expression \( a^x \) as \( a \) approaches infinity and \( x \) approaches zero. Participants explore the implications of this limit in the context of calculus and its relevance in fields such as Quantum Field Theory.

Discussion Character

  • Debate/contested
  • Mathematical reasoning

Main Points Raised

  • One participant suggests that the limit diverges as \( \ln a \), but they are unable to demonstrate this formally.
  • Another participant expresses uncertainty about the formal interpretation of the limit, referencing a known limit \( \lim_{x\to\infty}x^{1/x}=1 \) but noting it is not directly applicable.
  • A third participant cites a source indicating that different paths toward the limit can yield different values, implying that the limit does not exist.
  • One participant presents a calculation suggesting that the limit equals one, using L'Hôpital's rule to derive \( L = e^0 = 1 \).
  • Another participant proposes a specific substitution \( a = e^{1/x} \) and concludes that the limit approaches \( e \) when taking the limit from the positive side of \( x \), indicating that the path taken affects the outcome.
  • A participant notes that calculus textbooks classify \( \infty^0 \) as an indeterminate form, highlighting the complexity of the limit.
  • Another perspective is introduced regarding the rates at which \( a \) approaches infinity and \( x \) approaches zero, suggesting that this could lead to various outcomes, including finite numbers or non-existence of the limit.

Areas of Agreement / Disagreement

Participants do not reach a consensus on the limit, with multiple competing views presented regarding its existence and value depending on the approach taken.

Contextual Notes

The discussion reveals limitations in the assumptions about the rates at which \( a \) and \( x \) approach their respective limits, as well as the dependence on the paths taken in evaluating the limit.

ndung200790
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Please teach me this:
What is the limit of [a]^{x} when [a]\rightarrow[/infinity] and[x]\rightarrow[/zero].It seem to me that it is divergent as lna,but I can not demontrate.It appears in the renormalization of Quantum Field Theory.
Thank you very much in advanced.
 
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I am not sure how this limit should be interpreted formally.

We know that [itex]\lim_{x\to\infty}x^{1/x}=1[/itex], but it's not the same limit of course.
 
According to http://en.wikipedia.org/wiki/Multivariable_calculus:
"Since taking different paths toward the same point yields different values for the limit, the limit does not exist."
 
Last edited by a moderator:
The limit is one.
Lim(x,a -> 0,inf) a^x= L
lim x(lna)= ln(L)
lim (lna)/(1/x) = ln(L)
By l'hopital's, lim (1/a) / (-1/x^2) = ln(L)
lim(-x^2/a)=0=ln(L)
L=e^0=1
 
If we set a = e^(1/x) and take the limit from x to zero from the positive side, we get:

[tex]\lim_{a,x \to \infty,0} a^x = \lim_{x \downarrow 0} (e^{\frac 1 x})^x = \lim_{x \downarrow 0} e^1 = e[/tex]

In other words, it matters which path you take, so the limit does not exist.
 
Calculus textbooks say it this way: " [tex]\infty^0[/tex] is an indeterminate form ".
 
Another way to look at the OP's problem is the rate at which the exponent approaches infinity and the base approaches 0. Depending on the rates, this could approach some finite number, +/-infinity or not exist.
 
Last edited:

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