Exploring the Limit of $\displaystyle \frac{\infty}{\infty}$

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Further, L'Hopital's rule does not apply to this limit, as the numerator and denominator do not both approach infinity or both approach zero. Therefore, taking the natural logarithm on both sides allows us to manipulate the limit to a form where we can use L'Hopital's rule.
  • #1
karush
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$\displaystyle
L_b=\lim_{x \to \infty}
\left\{\frac{n^2}{2^n}\right\} \implies\frac{\infty}{\infty} \\
\text{take natural log of both sides} \\
\ln\left(L_b{}\right)=\lim_{x \to \infty}
\left\{\frac{2\ln\left({n}\right)}{n\ln\left({2}\right)}\right\} \\
\text{not sure?? } $
 
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  • #2
You need to prove that $2^n > n^2$ for large $n$.
 
  • #3
Why take logs? Why not simply apply L'Hopital's rule to the original limit twice?
 
  • #4
greg1313 said:
Why take logs? Why not simply apply L'Hopital's rule to the original limit twice?

$\text{thusly..}$
$$\displaystyle
L_b=\lim_{x \to \infty}
\left\{\frac{n^2}{2^n}\right\} $$

$$\displaystyle
L'_b=\lim_{x \to \infty}
\left\{\frac{2n}{2^{n}\ln\left({2}\right)}\right\} $$

$$\displaystyle
L''_b=\lim_{x \to \infty}
\left\{\frac{2}{2^n\ln\left({2}\right)^2}\right\} $$
$x \to \infty$
$$L_b=0$$

- - - Updated - - -

ZaidAlyafey said:
You need to prove that $2^n > n^2$ for large $n$.

Prove?
 
Last edited:
  • #5
You can use the mathematical induction.
 
  • #6
whatever that is?
 
  • #7
karush said:
$\displaystyle
L_b=\lim_{x \to \infty}
\left\{\frac{n^2}{2^n}\right\} \implies\frac{\infty}{\infty} \\
\text{take natural log of both sides} \\
\ln\left(L_b{}\right)=\lim_{x \to \infty}
\left\{\frac{2\ln\left({n}\right)}{n\ln\left({2}\right)}\right\} \\
\text{not sure?? } $
The logarithm of [tex]\frac{n^2}{2^n}[/tex] is not [tex]\frac{2ln(n)}{nln(2)}[/tex]. It is [tex]2ln(n)- n ln(2)[/tex].
 

FAQ: Exploring the Limit of $\displaystyle \frac{\infty}{\infty}$

What is the limit of $\displaystyle \frac{\infty}{\infty}$?

The limit of $\displaystyle \frac{\infty}{\infty}$ is indeterminate. This means that it does not have a definite value and the result can vary depending on the specific situation.

How do you explore the limit of $\displaystyle \frac{\infty}{\infty}$?

To explore the limit of $\displaystyle \frac{\infty}{\infty}$, you can use various mathematical techniques such as L'Hopital's rule or algebraic manipulation to simplify the expression and determine its behavior as the numerator and denominator approach infinity.

What are the common scenarios where the limit of $\displaystyle \frac{\infty}{\infty}$ arises?

The limit of $\displaystyle \frac{\infty}{\infty}$ often arises in calculus and other branches of mathematics when dealing with functions that have infinite values or infinite rates of change.

Why is the limit of $\displaystyle \frac{\infty}{\infty}$ important in mathematics?

The limit of $\displaystyle \frac{\infty}{\infty}$ is important because it allows us to determine the behavior of functions as they approach infinity, which is crucial in understanding the overall behavior and characteristics of these functions.

What are some real-life applications of the limit of $\displaystyle \frac{\infty}{\infty}$?

The limit of $\displaystyle \frac{\infty}{\infty}$ has various applications in physics, engineering, and economics. For example, it can be used to study the growth rate of a population, the speed of an object approaching infinity, or the rate at which a company's profits increase as their production approaches infinity.

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