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Math Help - Derivative

  1. #1
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    Derivative

    y= e^x / 4+ln2x

    find the derivative at x=1,
    f'(1)
    Last edited by john-1; April 30th 2010 at 03:17 PM.
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  2. #2
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    e^(i*pi)'s Avatar
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    Quote Originally Posted by john-1 View Post
    y=e^x/ (1+lnx)
    y' at x= 1 = 0

    Can someone confirm this for me?
    Standard quotient rule

    u = e^x \: \rightarrow \: u' = e^x

    v = 1+ \ln(x) \:\rightarrow\: v' = \frac{1}{x}

    y' = \frac{u'v-v'u}{v^2} = \frac{e^x(1+\ln x) - \frac{e^x}{x}}{(1+\ln x)^2}

    No idea what your condition means, I'm guessing y'(1) = 0

    Hence y'(1) = \frac{e - e}{1} = 0

    Note that y' = m. To find a co-ordinate sub in x=1 into y (not y')

    f(1) = e so we have the co-ordinate (1,e)


    You can now use the equation of a straight line which is y-y_1 = m(x-x_1)
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  3. #3
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    find the derivative at x=1,
    f'(1)

    I ended up getting 0.
    Last edited by john-1; April 30th 2010 at 03:15 PM.
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  4. #4
    Grand Panjandrum
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    Quote Originally Posted by john-1 View Post
    find the derivative at x=1,
    f'(1)

    I ended up getting 0.
    Which is wrong, did you use e^(i*pi)'s expression for the derivative?

    If not what did you use.

    CB
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