Why is the gamma function equal to (n-1) ?

In summary, the equality \Gamma(n) = (n-1)! is only true if n is an integer. The integral \Gamma(n) = \int^{\infty}_{0} x^{n-1} e^{-x}dx has a special property in calculus, requiring knowledge of integration. The Gamma function can be extended to non-integer numbers, and has a relationship to the "Runge phenomenon". It can be proven by induction that \Gamma(n) = (n-1)! using integration by parts.
  • #1
michonamona
122
0

Homework Statement



Why is the equality below true?

[tex]\Gamma(n) = (n-1)![/tex]

Where [tex]\Gamma(n) = \int^{\infty}_{0} x^{n-1} e^{-x}dx[/tex]

Homework Equations


The Attempt at a Solution



I've read the article on wikipedia but I cannot understand it. Is there any special properties in calculus that I must know in order to comprehend this?

Thank you
M
 
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  • #2
It is true only if n is integer

Solve:

[tex]\int_0^\infty t^{4-1}e^{-t} dt[/tex]

Compare if it's equal to
[tex](4-1)![/tex]

Gamma function is really beautiful beacuse it extends the concept of factorial out of integer numbers.
I've read the article on wikipedia but I cannot understand it. Is there any special properties in calculus that I must know in order to comprehend this?

Yep, being able to integrate. :()
 
  • #3
You can use integration by parts to show that

[tex]\Gamma(n) = (n-1)\Gamma(n-1)[/tex]

If n is an integer, you can use this to prove by induction that

[tex]\Gamma(n) = (n-1)![/tex]
 
  • #4
I went to a talk by John Chapman on this and he said said that the Gamma function is related to "Runge phenomenon".
 

Related to Why is the gamma function equal to (n-1) ?

1. Why is the gamma function equal to (n-1)?

The gamma function, denoted by Γ(n), is defined as the integral from 0 to ∞ of x^(n-1)e^(-x)dx. This integral can be used to generalize the factorial function to non-integer values. In other words, the gamma function is a way to extend the concept of factorial to real and complex numbers. Thus, the value of Γ(n) at integer values of n is equal to (n-1)!, which explains why the gamma function is equal to (n-1).

2. How is the gamma function related to the factorial function?

The gamma function is closely related to the factorial function. In fact, it can be seen as an extension of the factorial function to non-integer values. The value of Γ(n) at integer values of n is equal to (n-1)!, which makes the gamma function a useful tool in calculating factorial values for non-integer numbers.

3. What is the significance of the gamma function in mathematics?

The gamma function has many applications in mathematics, particularly in areas such as complex analysis, number theory, and probability. It is also used in physics and engineering, where it is used to solve certain differential equations and probability problems. Additionally, the gamma function is an important tool in statistical analysis, where it is used to calculate probabilities and confidence intervals.

4. Can the value of the gamma function be calculated for negative numbers?

Yes, the gamma function can be calculated for negative numbers. However, it is undefined for negative integer values, as this would result in division by zero. For non-integer negative values, the gamma function can be calculated using the identity Γ(-n) = (-1)^nΓ(n)/n, which allows for the calculation of the gamma function for any real or complex number.

5. How is the gamma function used in solving mathematical problems?

The gamma function has many practical applications in solving mathematical problems. It is commonly used to calculate probabilities, solve differential equations, and evaluate certain infinite series. In addition, the gamma function is an essential tool in many areas of mathematics, including number theory, complex analysis, and statistics.

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