Results 1 to 3 of 3

Math Help - Integration Problem!!

  1. #1
    Newbie
    Joined
    Feb 2011
    Posts
    18

    Integration Problem!!

    Hi,

    I've been working on the following problem- the question is to integrate the following



    dx/2xlog^18x.


    I have used substitution letting u= log x and therefore du=dx/x. When I integrate I get 1/2[u^-17/-17 + C].Subbing back in for u this gives me 1/2[log^-17x/-17 + C].

    We are asked to verify our answer by differentiating and seeing if we get the original function. However, when I differentiate I get 1/2[log^-18x] = 1/2log^18x. As you can see I am missing an x in the denominator.

    I would appreciate some help please!! Keep going over it but dont know where I'm going wrong. Thanks
    Follow Math Help Forum on Facebook and Google+

  2. #2
    MHF Contributor
    Joined
    Oct 2008
    Posts
    1,034
    Thanks
    49

    Re: Integration Problem!!

    Quote Originally Posted by orlacoon View Post
    when I differentiate... missing an x in the denominator.
    Not if you apply the chain rule for differentiation - the working backwards through which was the point of the sub.

    Would love to post a pic, have to dash - maybe later. Basically, the inner function is log x, and the chain rule tells you to multiply your derivative by the derivative of log x... voila!
    Follow Math Help Forum on Facebook and Google+

  3. #3
    Newbie
    Joined
    Feb 2011
    Posts
    18

    Re: Integration Problem!!

    Thanks a million! Seems so simple now!
    Follow Math Help Forum on Facebook and Google+

Similar Math Help Forum Discussions

  1. Integration Problem 2
    Posted in the Calculus Forum
    Replies: 4
    Last Post: April 5th 2010, 04:37 AM
  2. Replies: 2
    Last Post: February 19th 2010, 10:55 AM
  3. Integration problem
    Posted in the Calculus Forum
    Replies: 2
    Last Post: October 22nd 2009, 11:03 AM
  4. Integration problem?
    Posted in the Calculus Forum
    Replies: 6
    Last Post: June 3rd 2009, 06:33 PM
  5. Integration problem
    Posted in the Calculus Forum
    Replies: 5
    Last Post: April 1st 2008, 04:47 AM

Search Tags


/mathhelpforum @mathhelpforum