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Thread: Integral theory

  1. #1
    Jun 2008

    Integral theory

    Let S be the subset of x-axis consisting of the union of the open interval of length 1/4 centered at 1/2, and the open intervals of length 1/16 centered at 1/4 and 3/4, the open intervals of length 1/64 centered at 1/8, 3/8, 5/8, and 7/8, and so forth. Let U = S x (0,1) be the union of the open rectangles of height 1, based on these intervals. Thus U is the union of one rectangle of area 1/4, two rectangles of area 1/16, four rectangles of area 1/64, ... some of which overlap.

    show that the inner area of U is less than 1/2.

    My first approach was to sum the areas of each rectange...

    (ie) 1/4 + 2(1/8) + 4(1/6) ....

    however this is incorrect because the rectangles intersect.
    Any ideas/help?

    ahh.. stupid question, I see why none of you answered it.

    $\displaystyle \sum_{k=0} 2^{k} (\tfrac{1}{4^{k+1}}) \leq \sum \tfrac{1}{2^{k+2}} $
    Obviously this sum converges to 1/2.

    Of course the rectangles intersect so we over estimate the real inner area, so clearly the inner area is less than 1/2.

    HOWEVER the last part of this question is much more difficult.
    Let V = R/U. Show that V is a closed set whose ourter area is bigger than 1/2.

    help with the last part would be appreciated.
    Last edited by csuMath&Compsci; Dec 14th 2009 at 09:14 AM.
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