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Math Help - log 45

  1. #1
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    log 45

    If log 3 = x and log 5 = y, then rewrite log 45.
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  2. #2
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    e^(i*pi)'s Avatar
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    Quote Originally Posted by magentarita View Post
    If log 3 = x and log 5 = y, then rewrite log 45.
    45 = 3x3x5

    log(ab^2) = 2log(b) + log(a)
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  3. #3
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    are you.....

    Quote Originally Posted by e^(i*pi) View Post
    45 = 3x3x5

    log(ab^2) = 2log(b) + log(a)
    Are you saying for me to use the given formula?
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  4. #4
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    e^(i*pi)'s Avatar
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    Quote Originally Posted by magentarita View Post
    Are you saying for me to use the given formula?
    Yup, in this case:

    log(45) = log(9) + log(5) = \log(3^2) + log(5) = 2log(3) + log(5)

    Since you have log(3) = x and log(5) is y you will get log(45) = 2x +y
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  5. #5
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    Talking

    Quote Originally Posted by magentarita View Post
    Are you saying for me to use the given formula?
    You should have recognized this "formula" as an application of the basic log rules. (That is, they were supposed to have taught you the log rules before assigning this exercise.)

    To learn how to expand and "compress" log expressions as demonstrated in this and other threads, try here.
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  6. #6
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    ok

    Quote Originally Posted by e^(i*pi) View Post
    Yup, in this case:

    log(45) = log(9) + log(5) = \log(3^2) + log(5) = 2log(3) + log(5)

    Since you have log(3) = x and log(5) is y you will get log(45) = 2x +y
    I clearly see the substitution for log3 and log5 now.
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  7. #7
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    help

    the rules of logarithms are such that log(ab) = log a + log b
    log(a/b) = log a - log b
     log (a^b) = b \times log (a)
    Last edited by Mirado; April 20th 2009 at 10:42 PM. Reason: didn't see the others
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