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Math Help - Sum of series-Geometric?

  1. #1
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    Sum of series-Geometric?

    How do i show that

    \sum_{n=2}^{n}1/2^{n}\le0.5

    I know \sum_{k=0}^{\infty}r^k=\frac{1}{1-r} but the above starts from n=2 so can't work it out.

    thanks for any help.
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  2. #2
    Senior Member AllanCuz's Avatar
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    Quote Originally Posted by charikaar View Post
    How do i show that

    \sum_{n=2}^{n}1/2^{n}\le0.5

    I know \sum_{k=0}^{\infty}r^k=\frac{1}{1-r} but the above starts from n=2 so can't work it out.

    thanks for any help.
    \sum_{n=2}^{n}1/2^{n}=\sum_{j=0}^{n-2}1/2^{j+2}
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