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Math Help - [SOLVED] Geometric Sequence

  1. #1
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    [SOLVED] Geometric Sequence

    Im working on putting sequences in formulas. I have the sequence:
    X-X^3+X^5-X^7+X^9+....

    I see the difference in exponets is Plus 2, but how do I get the negative and positive terms?

    Thanks 4 Any help!!
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  2. #2
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    \sum\limits_k {\left( { - 1} \right)^{k + 1} x^{2k - 1} }
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  3. #3
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    Im sorry, I should have mentioned the sequence starts at 0 not 1. Would that answer still apply to the sequence?
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  4. #4
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    Hello, nikie1o2!

    I'm working on putting sequences in formulas. . not sure what this means

    I have the sequence: . x-x^3+x^5-x^7+x^9+\hdots

    I see the difference in exponents is Plus 2,
    but how do I get the negative and positive terms?

    If you are working with Geometric Series, then you want to identify
    . . the first term a, and the common ratio, r.

    In this problem, the first term is x, the common ratio is \text{-}x^2


    If you are trying to write the general term for the series, a_n,

    . . it looks like this: . a_n \:=\:(\text{-}1)^{n+1}x^{2n-1}

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  5. #5
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    Quote Originally Posted by nikie1o2 View Post
    Im sorry, I should have mentioned the sequence starts at 0 not 1. Would that answer still apply to the sequence?
    It does make a slight different.
    a_n=(-1)^n x^{2n+1}
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