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Math Help - integration

  1. #1
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    Exclamation integration

    I am having trouble solving this integration...I've tried about 10 times now and I'm getting the same answer but it's still wrong. help!

    Integral from 0 to 300 of: (80/(1+r))*(2*pi*r)


    thanks!
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  2. #2
    Eater of Worlds
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    Rewrite as 160{\pi}\left[\int_{0}^{300}dr-\int_{0}^{300}\frac{1}{r+1}dr\right]

    Now, it's rather straightforward.
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  3. #3
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    same problem..help!

    I did that...then I used substitution to solve and I get:

    160pi(300-(ln(301)-ln(1)))

    but that's still the wrong answer...am I doing something wrong?
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  4. #4
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    What makes you think it's wrong?

    160\pi \left[r\big|_{0}^{300} - ln(r + 1) \big|_{0}^{300}\right]

    = 160 \pi \left[(300 - 0) - (\ln301 - \ln1)\right]
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  5. #5
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    same problem...still: integration

    we turn in our answers into a website.. I turned in that answer and it says its wrong. I have more tries left but I don't know what I'm doing wrong
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  6. #6
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    Quote Originally Posted by amaya View Post
    I did that...then I used substitution to solve and I get:

    160pi(300-(ln(301)-ln(1)))

    but that's still the wrong answer...am I doing something wrong?
    You do realise that ln(1) = 0 ....? So maybe the answer has to be submitted as

    160 \pi (300 - \ln 301) .....
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