Proving the Limit of an Expression: \frac{n^n}{n!}

In summary, the conversation discusses the limit of the expression lim_{n\rightarrow\infty}\frac{n^n}{n!} and suggests using Stirling's approximation to prove it. The conversation also touches on taking the log of the term in the numerator and using the form n!~(n/e)^n or ln(n!)~n*ln(n)-n.
  • #1
ercagpince
30
0

Homework Statement


what is the limit of this expression?

[tex]lim_{n\rightarrow\infty}\frac{n^n}{n!}[/tex]

Homework Equations


The Attempt at a Solution


I tried to make it look like [tex]\frac{x^n}{n!}[/tex] and also tried to apply the sandwich theorem, but got nothing logical.
Probably the limit is [tex]\infty[/tex], still I want to prove it mathematically.
 
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  • #2
You could take the log and use Stirling's approximation on the factorial.
 
  • #3
Could you show it explicitly?
 
  • #4
ercagpince said:
Could you show it explicitly?

If you mean show the details, Isn't that your job? Did you look up Stirling's approximation? Or do you mean do it without Stirling's formula?
 
  • #5
if you take the stirling's approximation there is no need to take log of the term on numerator.
that why i asked that.
 
  • #6
ercagpince said:
if you take the stirling's approximation there is no need to take log of the term on numerator.
that why i asked that.

Right, if you use the form n!~(n/e)^n. I was thinking of ln(n!)~n*ln(n)-n
 
  • #7
thanks for the post
 

1. What does the limit of an expression represent?

The limit of an expression represents the value that the expression approaches as the independent variable approaches a certain value. It is a way to describe the behavior of a function at a specific point or as the input approaches a certain value.

2. How do you prove the limit of an expression?

To prove the limit of an expression, you need to show that for any small positive number, ε, there exists a corresponding positive number, δ, such that when the independent variable is within a distance of δ from the limiting value, the expression is within a distance of ε from the limiting value.

3. What is the significance of the expression n^n/n!?

The expression n^n/n! is significant because it represents the ratio of the growth rate of an exponential function (n^n) to the growth rate of a factorial function (n!). This ratio is important in understanding the behavior of many mathematical and scientific phenomena.

4. Can the limit of an expression be proven using algebraic manipulation?

No, the limit of an expression cannot be proven using algebraic manipulation alone. Algebraic manipulation can help in simplifying an expression and identifying its limiting value, but to prove the limit, we need to use the formal definition of a limit and show that it holds for all values of the independent variable.

5. How does the value of n affect the limit of the expression n^n/n!?

The value of n affects the limit of the expression n^n/n! because as n increases, the ratio of n^n/n! also increases. This means that the expression approaches infinity as n increases, and the limiting value will be infinity. Similarly, as n decreases, the expression approaches 0, and the limiting value will be 0.

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