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Math Help - Summation

  1. #1
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    Summation

    Thanks for taking the time to look at this, it's going to be one of those problems where I'm either missing something really obvious, or there's no simple way to approach it, so I thought I'd post it up on see if anyone has any ideas:

    From this summation:

    \sum^{b}_{x=1} f(x)g(x)

    I want to isolate \sum^{b}_{x=1} f(x), since I have a substitution for it.

    My question is then, is there a simple way to do this? The only way I can see is to sum each part in turn, multiply the 2 together, and then manually subtract the unwanted terms this also spews forth.

    Any help or thoughts would be appreciated, thanks again.
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  2. #2
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    Quote Originally Posted by Talamari View Post
    Thanks for taking the time to look at this, it's going to be one of those problems where I'm either missing something really obvious, or there's no simple way to approach it, so I thought I'd post it up on see if anyone has any ideas:

    From this summation:

    \sum^{b}_{x=1} f(x)g(x)

    I want to isolate \sum^{b}_{x=1} f(x), since I have a substitution for it.

    My question is then, is there a simple way to do this? The only way I can see is to sum each part in turn, multiply the 2 together, and then manually subtract the unwanted terms this also spews forth.

    Any help or thoughts would be appreciated, thanks again.
    Excuse me, but what do you mean by \sum^{b}_{x=1} f(x)g(x)? Are f and g defined over some countable set? That's the only case in which a sum makes sense. In any case, I don't see any way to separate f and g.
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