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Homework Help: Sigma notation

  1. Jun 9, 2007 #1
    1. The problem statement, all variables and given/known data
    I'm just having trouble seeing how the book is getting from point-to-point. I understand the area=height X Width part of the equation, but I don't see how in the seconds step (2i/5)(2/5) turns into [-(2i/5)^2+5](2/5). Smae goes for the second step in the second equation circled in red.
  2. jcsd
  3. Jun 9, 2007 #2


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    height is given by f(x) = f(2i/5) so you plug in x=2i/5:

    same goes for the second equation

    you have an expression for x as a function of i that you plug in to find f as a function of i.
  4. Jun 9, 2007 #3
    Ahh, now I see. I totally forgot about the f(x)=-x^2 equation. Thanks!
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