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Math Help - arithmetic series

  1. #1
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    arithmetic series

    calculate the sum of the first 50 terms.
    1+9+17+ ...
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  2. #2
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    Re: arithmetic series

    Use S_n = \frac{n}{2}(2a+(n-1)d)

    n=50 so,

    S_{50} = \frac{50}{2}(2a+(50-1)d)

    now all you need is 'a' the first term and 'd' the common difference from the series, what do you get?
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  3. #3
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    Re: arithmetic series

    thanks.
    and whats the geometric series forumla???
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  4. #4
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    Re: arithmetic series

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  5. #5
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    Re: arithmetic series

    what does the r represent?
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  6. #6
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    Re: arithmetic series

    Quote Originally Posted by ahmedb View Post
    what does the r represent?
    r is defined in the article linked by pickslides ... look for it.
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