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Math Help - find sum

  1. #1
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    find sum

    nb
    Last edited by oceanmd; December 13th 2007 at 05:31 AM.
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  2. #2
    is up to his old tricks again! Jhevon's Avatar
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    Quote Originally Posted by oceanmd View Post
    \sum_{n = 1}^{100} \ 3n-11

    Solution: a (first)= -8; a(100th) =289; Sum=14050

    Is this correct?
    Thank you
    that is correct. did you use the formula for the sum of the first n terms of an arithmetic series here? i suppose it can be done that way, but that's not what i did
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    is up to his old tricks again! Jhevon's Avatar
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    Quote Originally Posted by oceanmd View Post
    I used the formula S= n/2(a(first)+an(n-th term) This is Sum of Finite Arithmatic Series. What did you do?
    i used the fact that \sum_{i = 1}^{n}i = \frac {n(n + 1)}2

    so, \sum_{n = 1}^{100}3n - 11 = 3 \sum_{n = 1}^{100}n - \sum_{n = 1}^{100}11 = 3 \cdot \frac {100(101)}2 - 11(100) = \mbox{you know}
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