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Math Help - Log and nl stuff

  1. #1
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    Smile Log and nl stuff

    I keep on getting these wrong and I don't know what am I doing wrong for these problems:

    1. 1/3ln3 + 2ln3
    I first moved 1/3 and the equation becomes ln3^1/3 + ln3^2, after that I combined them and it becomes ln3^7/3. And that last step is where I was marked wrong.

    2. ln20 - ln5 - 2/3ln8
    I boiled down to ln4 - ln4 and after that I wrote 1 as final answer. It was marked wrong but I thought subtraction in ln means division?
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  2. #2
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    Quote Originally Posted by windia View Post
    1. 1/3ln3 + 2ln3
    I first moved 1/3 and the equation becomes ln3^1/3 + ln3^2, after that I combined them and it becomes ln3^7/3. And that last step is where I was marked wrong.
    Correct. But perhaps you were required to write it in the form {a}\ln{c}?
    [2. ln20 - ln5 - 2/3ln8
    I boiled down to ln4 - ln4 and after that I wrote 1 as final answer. It was marked wrong but I thought subtraction in ln means division?
    That's right. But when you perform the division, you get \ln\left(\dfrac{4}{4}\right) = \ln\left(1\right). Now, what's \ln\left(1\right)?
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  3. #3
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    Ahh I see lol
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  4. #4
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    Quote Originally Posted by windia View Post
    I keep on getting these wrong and I don't know what am I doing wrong for these problems:

    1. 1/3ln3 + 2ln3
    I first moved 1/3 and the equation becomes ln3^1/3 + ln3^2, after that I combined them and it becomes ln3^7/3. And that last step is where I was marked wrong.

    2. ln20 - ln5 - 2/3ln8
    I boiled down to ln4 - ln4 and after that I wrote 1 as final answer. It was marked wrong but I thought subtraction in ln means division?
    to #1: Your calculations seem to be OK, but your notation is horrible. Actually you should write the result as: ln(3^(7/3)).

    to #2: This term is quite ambiguous. You have to use brackets to be clear:

    (ln(20) - ln(5)) - 2/3ln(8) = \ln\left(\dfrac{\frac{20}{5}}{4}\right) = \ln(1)=0<br />

    ln(20) - (ln(5) - 2/3ln(8)) = \ln\left(\dfrac{20}{\frac54}\right)=\ln(16)
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  5. #5
    MHF Contributor Drexel28's Avatar
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    Quote Originally Posted by windia View Post
    I boiled down to ln4 - ln4 and after that I wrote 1 as final answer. It was marked wrong but I thought subtraction in ln means division?
    Did you forget that x-x=0?
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