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Math Help - rewrite log expression

  1. #1
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    rewrite log expression

    Hello, we rewrote this log expression:
    ln6 - ln15 + ln20

    to become
    ln(6/15 + 20)
    which was simplified to:
    ln(2/3 + 4)
    and which then:
    = ln 8.

    The problem is I cant see how the last step occurred eg. ln(2/3 + 4) becoming ln 8.
    Thank you for any help in understanding this step.
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  2. #2
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    Quote Originally Posted by fran1942 View Post
    Hello, we rewrote this log expression:
    ln6 - ln15 + ln20

    to become
    ln(6/15 + 20) no ... ln(6/15 * 20)
    ...
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  3. #3
    Junior Member mathfun's Avatar
    Joined
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    lna+lnb=ln(ab)
    lna-lnb=ln(a/b)

    So the given one is ln6-ln15+ln20=ln120-ln15=ln(120/15)=ln8
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