Limit as x approaches Infinity

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Homework Help Overview

The discussion revolves around evaluating the limit of the expression (1 + a/x)^x as x approaches infinity. Participants are exploring the implications of the exponent and the behavior of the expression as x increases.

Discussion Character

  • Exploratory, Assumption checking, Mathematical reasoning

Approaches and Questions Raised

  • Some participants attempt to analyze the limit by considering the behavior of the expression as x tends to infinity, noting that the base approaches one while the exponent tends to infinity. Others suggest using properties of limits and logarithms to reformulate the problem.

Discussion Status

There are multiple lines of reasoning being explored, with some participants providing detailed approaches involving logarithmic transformations and L'Hôpital's Rule, while others question the necessity of such methods. The discussion reflects a mix of interpretations regarding the limit's evaluation.

Contextual Notes

Participants are navigating through various definitions of the mathematical constant e and the implications of indeterminate forms that arise in the limit evaluation. There is a recognition of the complexity of the problem, as indicated by the differing opinions on the length and depth of the solution process.

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Homework Statement


Evaluate lim (1+a/x)^x
(that's limit as x tends to +infinity, sorry don't know how to latex that)

Homework Equations


The Attempt at a Solution


Stumped. Having that x exponent has my confused. As x tends to infinity I know what's inside the brackets will tend to one, but the exponent will make it tend to infinity. But the question has three marks to it, it can't be that simple.
 
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so
call your limit
f(a)
-show the the limit exists (the a=1 case should be familar)
-show f(x)f(y)=f(x+y)
-show f is continuous and differentiable at some point
now you should be able to identify f
 
Caesius, have you seen all definitions of e?

Oh and your latex that you wanted to do is \lim_{x \rightarrow \infty} which becomes \lim_{x \rightarrow \infty}
 
\lim_{x\rightarrow\infty}\left(1+\frac a x\right)^x

Set it equal to y, take the natural log of both sides.

y=\left(1+\frac a x\right)^x

\lim_{x\rightarrow\infty}\ln y=\lim_{x\rightarrow\infty}x\ln\left(1+\frac a x\right)

\lim_{x\rightarrow\infty}\ln y=\lim_{x\rightarrow\infty}x\ln\left(1+\frac a x\right)

Now you have an Indeterminate form of \infty\cdot0

Keep solving till you can apply L'Hopital's Rule on the right side, then you will have "solved for \ln y, so use algebra to solve for "y" and you're pretty much done.
 
DavidWhitbeck said:
Caesius, have you seen all definitions of e?
QUOTE]

No one has seen all definitions of e as there are an infinite number of them.
 
rocomath said:
\lim_{x\rightarrow\infty}\left(1+\frac a x\right)^x

Set it equal to y, take the natural log of both sides.

y=\left(1+\frac a x\right)^x

\lim_{x\rightarrow\infty}\ln y=\lim_{x\rightarrow\infty}x\ln\left(1+\frac a x\right)

\lim_{x\rightarrow\infty}\ln y=\lim_{x\rightarrow\infty}x\ln\left(1+\frac a x\right)

Now you have an Indeterminate form of \infty\cdot0

Keep solving till you can apply L'Hopital's Rule on the right side, then you will have "solved for \ln y, so use algebra to solve for "y" and you're pretty much done.


Thats a great solution but I think no need to go that long;

as x approaches infinity "(a/x)" equates 0 .

Hence : 1+0 = 1
 
mubashirmansoor said:
Thats a great solution but I think no need to go that long;

as x approaches infinity "(a/x)" equates 0 .

Hence : 1+0 = 1

And that is just wrong. Try reading the other posts, they did mention "e" several times for a good reason.
 
mubashirmansoor said:
Thats a great solution but I think no need to go that long;

as x approaches infinity "(a/x)" equates 0 .

Hence : 1+0 = 1
Indeterminate Power of form: 1^{\infty} so yes it is necessary.
 

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