Show that the Gamma function is converging

In summary, the conversation is about the gamma function and how it is defined for n\geq1 by \Gamma(n)=\int_0^{\infty} t^{n-1}e^{-t}dt. The conversation also includes a discussion on how to show that the integral converges on n\geq1, and how to use integration by parts to find solutions for parts (b) and (c). Ultimately, the issue is resolved by using a comparison test to show convergence.
  • #1
crybllrd
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Homework Statement



The gamma function, which plays an important role in advanced applications, is defined for

[itex]n\geq1[/itex] by [itex]\Gamma(n)=\int_0^{\infty} t^{n-1}e^{-t}dt[/itex]

(a) Show that the integral converges on [itex]n\geq1[/itex]

(b) Show that [itex]\Gamma(n+1)=n\Gamma(n)[/itex]

(c) Show that [itex]\Gamma(n+1)=n! if n\geq1[/itex] is an integer

The Attempt at a Solution



I am only having trouble with part (a)

(a) I used integration by parts to get

[itex]e^{-t}nt^{n}+\int_0^{\infty} t^{n}e^{-t}dt[/itex]

I also tried it with a different u and dv:

[itex]-t^{n-1}e^{-t}+(n-1)\int_0^{\infty} t^{n-2}e^{-t}dt[/itex]

I used this second IBP to find part (b), which I used for (c).

How can I show it is converging?
 
Last edited:
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  • #2
Never mind, I figured it out with a comparison test.
Funny, after I post things on here I always seem to figure them out on my own.
Well, whatever works!
 

1. What is the Gamma function?

The Gamma function is a mathematical function that is used to extend the concept of factorial to non-integer values. It is denoted by the Greek letter Γ (gamma) and is defined as Γ(z) = ∫0 xz-1e-xdx.

2. How is the Gamma function related to factorial?

The Gamma function is closely related to the factorial function, as it is an extension of it to non-integer values. For positive integers, Γ(n) = (n-1)!. However, for non-integer values, the Gamma function allows us to calculate values such as ½! = √π/2.

3. Why is it important to show that the Gamma function is converging?

It is important to show that the Gamma function is converging because it allows us to use it in various mathematical calculations. Convergence means that the function approaches a finite value as the input approaches a certain value. In the case of the Gamma function, this value is ∞, and showing convergence ensures that the function is well-defined for all values of z.

4. How is the convergence of the Gamma function proven?

The convergence of the Gamma function is proven using the integral definition and various mathematical techniques, such as the comparison test, the ratio test, or the limit comparison test. These techniques are used to show that the integral of the function converges, which in turn proves that the function itself is converging.

5. What are some applications of the Gamma function?

The Gamma function has many applications in mathematics, physics, and engineering. It is used to calculate complex integrals, solve differential equations, and evaluate series expansions. It is also used in probability and statistics, such as in the gamma distribution. In addition, the Gamma function has applications in quantum mechanics, number theory, and even in the field of computer graphics.

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