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!

Integral problem

  1. Oct 4, 2004 #1
    I have this integral: (The first is the original, the one I need to solve)
    http://www.absinthen.dk/math.jpg [Broken]

    Well, I have a program that can calculate it for me, but I need to do it in hand - but even though I keep trying, I just don't end up with the result my program says it is, which is:
    2*e^sqrt(x)-2*e

    I've been trying everything, but I going crazy very soon :cry:

    I really hope you guys can give me a hint, of what may be wrong.


    - Ylle
     
    Last edited by a moderator: May 1, 2017
  2. jcsd
  3. Oct 4, 2004 #2
    I don't understand exactly what it is you've done to the integral, but...

    [tex]\int e^{\sqrt{x}} x^{-1/2} dx = \int e^{\sqrt{x}} \cdot \frac{dx}{\sqrt{x}}[/tex]

    Let [tex]u = \sqrt{x}[/tex]. Then [tex]\frac{du}{dx} = \frac{1}{2} \cdot \frac{1}{\sqrt{x}}[/tex], so 2du = 1/sqrt(x) dx. The integral turns in to:

    [tex]\int e^{u} \cdot 2 du[/tex]

    After finding an antiderivative, putting in the limits should be easy... ;)
     
    Last edited: Oct 4, 2004
  4. Oct 4, 2004 #3
    hehe, and i don't understand what you are doing :D
    I don't think they teach us to solve the integral the same way, as they do to you :(

    But another example:
    http://www.absinthen.dk/math2.jpg [Broken]

    This integral is solved correctly this time, and I've done the same thing as I would do in the one I gave you. But in the one I gave you, it just wont do as I want it to do :confused:
     
    Last edited by a moderator: May 1, 2017
  5. Oct 4, 2004 #4

    HallsofIvy

    User Avatar
    Staff Emeritus
    Science Advisor

    I really doubt that anyone "taught" you to replace "x" with "t" without saying what in the world the relationship between x and t is!

    I also note that when you make the substitution, there is no "dt" in the integral. You are not being sufficiently careful- that may be where your problem is.

    State clearly what substitution you are making and how you are replacing dx.
     
    Last edited: Oct 5, 2004
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook




Similar Discussions: Integral problem
  1. Integration problem (Replies: 17)

  2. Problem with integration (Replies: 16)

  3. Integration Problem (Replies: 1)

  4. Integral problem (Replies: 2)

  5. Integral Problem (Replies: 1)

Loading...