Probability - u substitution to find gamma function.

In summary, the gamma function is a mathematical function used to extend the factorial function to non-integer values. It can be found using various methods, including u substitution, and has applications in various fields such as statistics, physics, and number theory. Some special values of the gamma function include 1, √π, and ∞.
  • #1
sirhc1
4
0

Homework Statement



[itex]\int_0^∞ x^2exp(-x/2) dx[/itex]

Homework Equations



afe9f86ae39cdf0260aad124aac4a3e9.png


The Attempt at a Solution



Using u substitution:

u = x/2
du = 1/2 dx

[itex]\int_0^∞ 4u^2exp(-u) du*2[/itex]
= 8 [itex]\Gamma(3)[/itex]
= 8*3!
= 48

But the correct answer is 16 when I plug it in Wolfram's definite integral calculator. I don't see where's my mistake?

Thank you very much!
 
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  • #2
Wow, Gamma(3) = 2!, not 3!. Silly me! Thanks anyways.
 

FAQ: Probability - u substitution to find gamma function.

What is the gamma function?

The gamma function, denoted by the symbol Γ(n), is a mathematical function used to extend the factorial function to non-integer values. It is defined as Γ(n) = (n-1)! for positive integer values of n, and can be extended to all complex numbers except for negative integers.

How is u substitution used to find the gamma function?

U substitution is a technique used in calculus to simplify integration problems. In the context of finding the gamma function, u substitution can be used to transform the integral into a more manageable form. This involves substituting u = x^(n-1) and expressing the gamma function in terms of u, which can then be solved using standard integration techniques.

What are the applications of the gamma function?

The gamma function has various applications in mathematics and science. It is commonly used in statistics and probability to calculate the area under a gamma distribution curve. It is also used in complex analysis, number theory, and in solving differential equations. Additionally, the gamma function has applications in physics, particularly in quantum mechanics and quantum field theory.

Can the gamma function be calculated without using u substitution?

Yes, the gamma function can also be evaluated using other methods such as the Lanczos approximation or the Stirling's formula. However, u substitution is a commonly used technique as it simplifies the integration process and can be applied to a wide range of problems.

Are there any special values of the gamma function?

Yes, there are several special values of the gamma function that are frequently used in mathematical calculations. These include Γ(1) = 1, Γ(1/2) = √π, and Γ(n) = (n-1)! for positive integer values of n. The gamma function also has a value of ∞ for negative integer values of n and for 0.

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