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Homework Help: Help with Integral Proof

  1. Apr 16, 2008 #1
    I have posted a problem from my book below. I am having trouble with a homework problem similar to this one and can't, for the life of me, figure it out. The back of the book says the ansewer to this problem is 4/3. I can't figure how they're getting that. I've tried everything I can think of, and I'm not even close.

    Could someone explain how to solve this problem? I hate to post it with no solution attempt, but I am lost.

    Please excuse the sorry attempt at using LaTex..I wrote it out the best I could. Obviously, n is above Sigma and i = 1 is under it.

    1. The problem statement, all variables and given/known data

    Use the form of the defenition of the integral given in Theorem 4 to evaluate the integral.

    [tex]\int[/tex][tex]\stackrel{2}{0}[/tex] (2-x^2)dx

    2. Relevant equations

    Theorem 4 states that:

    "If f is integrable on [a,b], then the following is true:

    [tex]\int[/tex][tex]\stackrel{b}{a}[/tex] f(x)dx = lim as n --> [tex]\infty[/tex] [tex]\sum[/tex][tex]\stackrel{n}{i=1}[/tex] f(x sub i)[tex]\Delta[/tex]x

    where [tex]\Delta[/tex]x = (b-a)/n and x sub i = a + i[tex]\Delta[/tex]x

    3. The attempt at a solution

    The answer is 4/3.

    [tex]\Delta[/tex]x = (2-0)/n = 2/n

    x sub i = a + i[tex]\Delta[/tex]x = 0 + (2/n)i

    That's all I have that I know is right..
    Last edited: Apr 16, 2008
  2. jcsd
  3. Apr 16, 2008 #2


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    Alright, so what do you get when you put those values into the formula of theorem 4?

    Click on this to see the code i used:

    [tex]\int_a^bf(x)dx = \lim_{n\rightarrow +\infty}\sum_{i=1}^nf(x_i)\Delta x[/tex]
  4. Apr 17, 2008 #3
    Alright, I finally figured it out. Now I feel like an idiot.

    Thanks for the Tex code.
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