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Summation question

  1. Jan 20, 2014 #1

    joshmccraney

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    Gold Member

    hey pf!

    can someone explain to me what to do if presented with an equation like this: [tex]\sum_{i=1}^{n}A_i=i[/tex]
    is this identical to stating [itex]A_i=i[/itex]? either way, can you please explain.

    thanks!

    josh
     
  2. jcsd
  3. Jan 20, 2014 #2

    Mark44

    Staff: Mentor

    It doesn't make much sense to me. On the left side, i is an index variable that takes on the values 1, 2, 3, ..., n, so I have no idea what it means on the right side.

    Where did you see this? If it's from a textbook, can you post a picture?
     
  4. Jan 20, 2014 #3

    AlephZero

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    Science Advisor
    Homework Helper

    Just taking it at face value, it means
    ##A_1 + A_2 + \cdots + A_n = i##

    The ##i## in the sum is a "bound variable" or "dummy variable". You could replace it by anything else (except ##n##) without changing the meaning. The ##i## on the right hand side means ##i##.

    But using ##i## twice in one equation like that is horrible, as Mark44 said. It would have been more literate to write something like
    $$\sum_{k=1}^n A_k = i$$
     
  5. Jan 20, 2014 #4

    joshmccraney

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    Gold Member

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