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Thread: negative logs

  1. #1
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    negative logs

    "Explain why it is not possible to use the product law of logarithms to evaluate the expression log(-7) + log(-4)?"

    I had a TIPS/Comm assignment yesterday, and i had this question. I didn't know how to answer it, except that you can't evaluate xlog(y) with y < 0 .. how would you guys do it?
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  2. #2
    Super Member bigwave's Avatar
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    well this isn't a formal proof but...
    $\displaystyle
    y = log_{a}(x)\$ means $\displaystyle \ x = a^y$

    so if $\displaystyle a$ is taken to a postive or negatve exponent $\displaystyle x$ will always be positive

    example

    $\displaystyle 2^3 = 8\ \ 2^{-3} = .1250 $
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