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Math Help - natural log differentiating problem, thanks

  1. #1
    Member dokrbb's Avatar
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    differentiating (ln u)^(f) in x = a

    I have to evaluate d/dx of (ln (5 x^(2)))^(1/4) at x = 1

    So, differentiating it I proceeded by y= (ln (5 x^(2)))^(1/4) = (ln (5 x^(2)))^(3-/4) * 1/(5 x^(2)) * (-2x) = (ln (5 x^(2)))^(3-/4) *(-2x)/(5 x^(2));

    By calculating this for x=1 gives me such a odd number, I am pretty sure I am wrong when I operate with the logarithmic values (since there I found after my mid-term that I have some gaps);

    Could you take a look at it, and also give some links where I would be able revise some basic knowledge on logarithms?

    Greatly appreciated,
    Last edited by dokrbb; February 28th 2013 at 06:43 AM. Reason: look for another format to write the formulas
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  2. #2
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    Re: natural log differentiating problem, thanks

    You should get -\frac{1}{8(\ln{4})^\frac{3}{4}} or approximately -0.0978. Your derivative looks good (except you should have -3/4 instead of 3-/4).

    - Hollywood
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  3. #3
    Member dokrbb's Avatar
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    Re: natural log differentiating problem, thanks

    oh, this was a typo (3-/4), but yes, thanks a lot - I was doing a dumb mistake - forgetting to multiply 1/4 from the first with the (-1/2) from the last, and just working with 4*(...) instead of 8*(...)

    Thanks a lot
    Last edited by dokrbb; February 28th 2013 at 07:02 AM.
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