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Math Help - log. problems

  1. #1
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    log. problems

    a) log9 1/81= x

    b) logx81=4
    Last edited by robinpatrick; October 23rd 2006 at 07:39 PM.
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  2. #2
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    #1 has something missing.

    #2) \log_{x}81=4

    Thus x^4=81

    I don't know exactly what method your teacher wants you to solve these, but this one works out nicely as 3.
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  3. #3
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    Hello, robinpatrick!

    Rewrite in exponential form . . .


    a)\;\log_9\left(\frac{1}{81}\right) \:=\:x

    We have: . 9^x\:=\:\frac{1}{81} \:=\:\frac{1}{9^2}

    Then: . 9^x\:=\:9^{-2}\quad\Rightarrow\quad x = -2



    b)\;\log_x(81)\:=\:4

    We have: . x^4\:=\:81

    Then: . x^4\:=\:3^4\quad\Rightarrow\quad x = 3

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