Results 1 to 3 of 3

Math Help - A simple ln differentiation question

  1. #1
    Newbie
    Joined
    Oct 2009
    Posts
    17

    A simple ln differentiation question

    Hi

    I'm somewhat embarassed to be asking such a simple question but hopefully someone would be kind enough to help me out.

    I've been asked to find the first and second derivatives of A = ln x so I got the following, which agreed with the answers given:

    A' = 1/x


    However, my confusion is with the second derivative. I prefer to use x^-1 rather than 1/x. Using x^-1 would give me -1*x^-1-1:

    A'' = -x^-2 or -1/x^2

    The answer given is 1/x^2 (ie positive, rather than the negative answer I get).

    Would somebody be kind enough to tell me which is correct and, if I'm wrong, please explain where I've gone wrong. Thanks very much.


    Dave.
    Follow Math Help Forum on Facebook and Google+

  2. #2
    Super Member
    Joined
    Jan 2008
    Posts
    588
    Thanks
    87
    You are correct.
    Follow Math Help Forum on Facebook and Google+

  3. #3
    Newbie
    Joined
    Oct 2009
    Posts
    17
    Thank you.

    I assumed that the lecturers answers would be correct so I've been trying to work out why my answer is wrong for ages. Oh well, at least I've got it right.

    Thanks again, your help is much appreciated.


    Dave.
    Follow Math Help Forum on Facebook and Google+

Similar Math Help Forum Discussions

  1. Replies: 3
    Last Post: December 22nd 2010, 03:21 AM
  2. Simple Differentiation Question
    Posted in the Calculus Forum
    Replies: 7
    Last Post: January 23rd 2010, 11:08 PM
  3. Simple Differentiation
    Posted in the Calculus Forum
    Replies: 5
    Last Post: November 25th 2009, 01:15 PM
  4. Replies: 2
    Last Post: November 12th 2009, 03:09 PM
  5. A simple differentiation
    Posted in the Calculus Forum
    Replies: 2
    Last Post: April 30th 2009, 06:59 AM

Search Tags


/mathhelpforum @mathhelpforum