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Math Help - summations

  1. #1
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    summations

    Hello,
    I am having difficulty solving a summation because both the upper bound is a different variable than the lower bound. The summation is as follows:

    2n
    E (i) = ?
    i=5

    The "E" represents the sigma. I had considered the following:
    5(0)n + 5(1)n + 5(2)n = 15n
    but I honestly have no idea if that is correct. Please let me know if I am on the right track. Thank you!
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  2. #2
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  3. #3
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    That makes perfect sense. Thank you very much!
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  4. #4
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    Ok, so how about one more...

    n-7
    E 2i + 7
    i=0
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  5. #5
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    Quote Originally Posted by collegestudent321 View Post
    Ok, so how about one more...
    n-7
    E 2i + 7
    i=0
    \sum\limits_{i = 0}^{n - 7} {2i + 7}  = 2\sum\limits_{i = 0}^{n - 7} {i + } \sum\limits_{i = 0}^{n - 7} 7  = 2\left( {\frac{{\left( {n - 7} \right)\left( {n - 6} \right)}}<br />
{2}} \right) + 7\left( {n - 6} \right)

    Note that as i=0,\cdots n-7 gives n-6 terms.
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  6. #6
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    Ok, the (n-6) terms part had me confused for a little but i got it now. Thank you once again for your help!
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