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Math Help - Differentiating exponential and logarithmic functions

  1. #1
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    Differentiating exponential and logarithmic functions

    Determine the equation of the tangent to the graph of y=log(lnk).

    My answer:

    1/(lnkln10)

    just can someone confirm this plz
    Last edited by john-1; May 2nd 2010 at 07:03 AM.
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  2. #2
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    Your solution for the equation of the tangent line is correct. The x-intercept is the value of x when y=0. In our case,

    0=kx_0+\ln\frac{1}{k}-1.

    Hope this helps!
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  3. #3
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    so then how do i solve for k?
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  4. #4
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    because the x is there
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  5. #5
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    Quote Originally Posted by john-1 View Post
    so then how do i solve for k?
    hi

    kx - ln k -1=0

    x=\frac{1+\ln k}{k}>0

    so k would be k<0 or k>1/e

    but k<0 is not acceptable because ln (<0) is undefined .

    Do the same to determine the set of values of k so that x is negative .
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