1. Limited time only! Sign up for a free 30min personal tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Integration Question

  1. Dec 6, 2014 #1
    1. The problem statement, all variables and given/known data
    Using [tex]\int_{-\infty}^{\infty}e^{-x^2/2} dx = \sqrt{2\pi}[/tex], Integrate x^(5/2) e^(-x) dx from 0 to infinty

    2. The attempt at a solution

    I tried substituting x = u^2/2 but i could not simplify further.
    Please help me with the problem.
    Thank you in advance.
     
    Last edited by a moderator: Dec 6, 2014
  2. jcsd
  3. Dec 6, 2014 #2

    Orodruin

    User Avatar
    Staff Emeritus
    Science Advisor
    Homework Helper
    Gold Member

    You are supposed to use the knowledge of the result of the given integral to find out the integral you want. Changing the integral to one with ##-x## in the exponent instead of ##-x^2/2## is a good start. I also suggest looking up Feynman's trick of differentiating an integral with respect to a parameter (not the integration variable) and changing the order of integration and differentiation.
     
  4. Dec 6, 2014 #3
    Thanks a lot feynman's trick was a good read. But if suppose i did have to use the given result then, what would be the method to go forward with?
     
  5. Dec 6, 2014 #4

    Orodruin

    User Avatar
    Staff Emeritus
    Science Advisor
    Homework Helper
    Gold Member

    I would use Feynman's trick together with the given result. The alternative is doing partial integration. It all is going to boil down to evaluation of the given integral in the end.
     
  6. Dec 6, 2014 #5
    I was just trying it i understood how it works. I should be able to use both together. Thanks a lot.
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?
Draft saved Draft deleted



Similar Discussions: Integration Question
  1. Integration question. (Replies: 10)

  2. Integral Questions (Replies: 2)

  3. Integration question (Replies: 2)

  4. Integral Question (Replies: 5)

  5. Integral Question (Replies: 8)

Loading...