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Math Help - series (serious!)

  1. #1
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    series (serious!)

    need help with series please:

    determine the values of the series <E(thats sposed to be a sigma) k=0 to oo (1/2)^k

    so what do i actually need to do because it goes up to infinity, you cant just solve each term and add them, what is the startergy to doing this? thank you kindle
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  2. #2
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    \displaystyle \sum_{k = 0}^{\infty}\left(\frac{1}{2}\right)^k is a geometric series with \displaystyle a = 1 and \displaystyle r = \frac{1}{2}.

    As long as \displaystyle |r| < 1 (as it is in this case) the infinite sum of a geometric series is equal to \displaystyle \frac{a}{1- r}.
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  3. #3
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    Quote Originally Posted by mathcore View Post
    need help with series please:

    determine the values of the series <E(thats sposed to be a sigma) k=0 to oo (1/2)^k

    so what do i actually need to do because it goes up to infinity, you cant just solve each term and add them, what is the startergy to doing this? thank you kindle
    It is a convergent geometric series, you use the formula for the sum in your notes and/or text.

    CB
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    \displaystyle \sum_{k=0}^{\infty}\left(\frac{1}{2}\right)^k = \sum_{k=0}^{\infty}x^k\bigg|_{x=\frac{1}{2}} = \frac{1}{1-x}\bigg|_{x=\frac{1}{2}} = \cdots
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  5. #5
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    i dont have "notes and/or text" as u put it

    does it make a difference whether k = 0 to infinite or k=1 to infite? why is a =1?

    is the answer 2?

    also, is a=1 because thats the first term (as its a zero power). if its a different first term, do you just dddddddddd
    Last edited by mr fantastic; January 3rd 2011 at 01:24 PM. Reason: Merged posts and editing.
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    Yes, \displaystyle a = 1 and the sum \displaystyle = 2.
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  7. #7
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    Quote Originally Posted by mathcore View Post
    Is the answer 2?

    also, is a=1 because thats the first term (as its a zero power). if its a different first term, do you just dddddddddd
    yes, the sum of the infinite geometric series \displaystyle \sum_{k = 0}^{\infty} \left(\frac{1}{2}\right)^k = 2

    a = 1 because the first term of the series is \displaystyle \left(\frac{1}{2}\right)^0 = 1.

    if the series started with k = 1 , then \displaystyle a = \frac{1}{2}

    here is a link for more info since you have no text or notes ...

    3. Infinite Geometric Series
    Last edited by mr fantastic; January 3rd 2011 at 01:24 PM.
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