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Homework Help: We're working with logarithms of base 3

  1. Feb 10, 2012 #1
    1. The problem statement, all variables and given/known data
    We're working with logarithms of base 3, and log(4)=a and log(7)=b.
    The goal is to put log(21) in terms of a and b. For example, take the log(112). It's the same thing as 2a+b since 4*4*7 = 112.

    2. Relevant equations

    Just the standard log properties.

    3. The attempt at a solution

    The only thing I could come up with is 1 + b log(3) = 1. I've been using Matlab to try to figure out a way to create 21 using a product and/or quotient of powers of 7 and 3 but have been unable to do so.
  2. jcsd
  3. Feb 10, 2012 #2


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    Re: Logarithms

    21 = 3 * 7, and you know log(7) and log(3).
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