Results 1 to 6 of 6

Math Help - Differentiation Problem for a forum newbie :)

  1. #1
    Newbie
    Joined
    Nov 2009
    Posts
    8

    Differentiation Problem for a forum newbie :)

    Hi,

    I was wondering if someone could explain how I get from A to B on this problem? I know it involves the product rule, but I'm not sure how to correctly apply it?


    I'm not sure how you display formulas, so I have attached a file.

    Thanks so much for any help you can give me
    Attached Files Attached Files
    Follow Math Help Forum on Facebook and Google+

  2. #2
    Junior Member
    Joined
    Nov 2009
    Posts
    31
    General rule:

    f(x)g(x) = f'(x)g(x) + f(x)g'(x)

    So if you have tow functions, first take derivative of the first multiplied by the second function then add the function of the first times the derivative of the second.

    Just like in your file is done.
    Follow Math Help Forum on Facebook and Google+

  3. #3
    Newbie
    Joined
    Nov 2009
    Posts
    8
    Hi,

    thanks for you reply - I'm still not totally clued up. Could you explain how this problem is broken down? I'm not sure why DS/DT ends up in the solution. What are the f'(x) g(x) f(x) g'(x) in the problem?

    If you could explain that, I would really appreciate it :-)
    Follow Math Help Forum on Facebook and Google+

  4. #4
    Junior Member
    Joined
    Nov 2009
    Posts
    31
    Hi,

    The total function where you want the derivative from is:
    pS_{T}e^{-iT}

    There are two functions of T in this expression:
     f(T) = S_{T}
    and
     g(T) = e^{-iT}

    Now use the rule and you should get the same result as in your document.

    And dS/dT is just the derivative of S_{T} with respect to T.

    Let me know if you can take it from here!

    Bye
    Follow Math Help Forum on Facebook and Google+

  5. #5
    MHF Contributor
    Joined
    Oct 2008
    Posts
    1,034
    Thanks
    49
    I found your picture rather unsettling, but assumed it must be explained by some esoteric notation. However, if

    Quote Originally Posted by jeneverboy View Post
     f(T) = S_{T}
    is right, then I think jeneverboy maybe just scanned the beginning and end, which are OK if we're to understand the derivative is set to zero, but didn't notice those unwanted (?) bracketed expressions in lines 2 and 3 - which are what I take it are confusing me and you, Karty. Typo? Where's it from?
    Follow Math Help Forum on Facebook and Google+

  6. #6
    Newbie
    Joined
    Nov 2009
    Posts
    8
    thank you both for your help.

    the problem is related to forrestry economics.

    i think the brackets were due to a previous simplification if I understand correctly.

    I've updated by document to show all calcs.

    I think I understand now.

    to confirm

    F'(T)=DS/Dt and G'(T)=D/Dte^-iT


    Thanks so much for the help.

    Katy
    Attached Files Attached Files
    Follow Math Help Forum on Facebook and Google+

Similar Math Help Forum Discussions

  1. Which forum, if any, is appropriate for this problem?
    Posted in the Discrete Math Forum
    Replies: 3
    Last Post: December 27th 2010, 01:10 AM
  2. SVD newbie - a simple problem
    Posted in the Advanced Algebra Forum
    Replies: 0
    Last Post: September 1st 2010, 07:54 AM
  3. Replies: 9
    Last Post: December 15th 2007, 11:14 AM
  4. Replies: 5
    Last Post: June 23rd 2006, 09:13 AM

Search Tags


/mathhelpforum @mathhelpforum