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Math Help - help with lo equation

  1. #1
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    help with lo equation

    hi, after 30 years from leaving school, ive decided to to a night class in engeineering and weve just started a module on maths. but im finding the maths very difficult. one of the questions is simplyfy 36 x 42 / 56 . using the log laws. ive never done logs before and im trying to read about them but i keep getting confused. Any help would be appreciated.
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  2. #2
    Member mohammadfawaz's Avatar
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    The main formulas you need here are the following:
    ln(ab) = ln(a)+ln(b)
    ln(\frac{a}{b}) = ln(a)-ln(b)
    ln(a^c) = cln(a).
    In the example you gave, take the logarithm: you get the following:
    ln(\frac{36\times 42}{56}) = ln(36)+ln(42)-ln(56)
    Now decompose each number using its prime factorization:
    you get: ln(2^2\times 3^2)+ln(2\times 3\times 7)-ln(2^3 \times 7) = 2ln(2)+2ln(3)+ln(2)+ln(3)+ln(7)-3ln(2)-ln(7) = 3ln(3)=ln(3^3) = ln(27).
    Hence, the number you need is 27.

    Hope this helps
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  3. #3
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    log(27) = 3.2958....

    log(36) * log(42) / log(56) = 3.3274....

    ?
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  4. #4
    Member mohammadfawaz's Avatar
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    <br /> <br />
ln(\frac{36\times 42}{56}) = ln(36)+ln(42)-ln(56) and not  \frac{ln(36)*ln(42)}{ln(56)}
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  5. #5
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    Agree if looked at that way; I guess it depends HOW one reads the problem...

    Thanks Mr Fawaz.

    The original post: simplyfy 36 x 42 / 56 . using the log laws.
    You don't need log laws to simplify 36 * 42 / 56: simple calculation...
    By the way, 36 * 42 / 56 = 27 : comments?
    Last edited by Wilmer; May 4th 2010 at 07:57 AM. Reason: add last question
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  6. #6
    Member mohammadfawaz's Avatar
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    Hehehehe, I was sure that what you posted was kind of for fun and that you were not actually wondering how the results are different, and that is based on the number of posts and thanks you have. I replied to your post to avoid confusion since lukebushnell has never done logs before.
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  7. #7
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    Quote Originally Posted by mohammadfawaz View Post
    Hehehehe, I was sure that what you posted was kind of for fun...
    Yes Mohammad, it sort of was: I really was trying to show the poster
    that his question was quite UNCLEAR...
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