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Math Help - Area between the curve?

  1. #1
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    Sep 2008
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    Area between the curve?

    I keep on getting the wrong answer on this problem..

    Find the area between the curves of y=lnx and the line y = x-2, the answer is 1.949, but I always get 1.917...

    So I used the problem as a dy problem, thus x = e^y, Y1, and x = y+2, Y2..

    I took the integral from -2 to 1 of Y2 - Y1 and I got 1.917, what am I doing wrong?
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  2. #2
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    Sep 2008
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    Nevermind, I figred it out.. The limits of integration were the two intersection points of both of the graphs.
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  3. #3
    Super Member
    Joined
    Jan 2009
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    I suppose there is only one way to solve:
    using software to find out the two intersections of the curves
    y=lnx and y=x-2
    Thank you for Winplot .. i can find out the points by using it and they are
    (0.15859 , -1.84141) and (3.14619 , 1.14619)
    The next step should be integrating lnx - (x-2)
    The result is xlnx + x - x^2/2
    Sub. these values and the ans is 1.949 (4 sfg)
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