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Math Help - Washer Method example question (please help!!)

  1. #1
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    Washer Method example question (please help!!)

    Let R be the region enclosed by the graph of y=√x-1 and x=10 and the x axis

    b) find the volume of the solid generated when R is revolved about the horizontal line y=3


    I thought it would be

    3.14 X the integral from 1 to 10 of (3) - (3-√x-1)

    according to my answer key, it is instead

    (3) - (√x-1 -3)

    I really don't get this. 3 is above √x-1 so why wouldn't you do 3 - √x-1 instead of √x-1 -3 (which would give a negative number)

    Please help guys, maybe my answer key is wrong?

    Thanks.
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  2. #2
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    Re: Washer Method example question (please help!!)

    Just for the record (3 - \sqrt{x - 1})^2 = ( \sqrt{x - 1} - 3)^2

    -Dan
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    Re: Washer Method example question (please help!!)

    Quote Originally Posted by topsquark View Post
    Just for the record (3 - \sqrt{x - 1})^2 = ( \sqrt{x - 1} - 3)^2

    -Dan

    well that's embarassing.

    Thanks.
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    Forum Admin topsquark's Avatar
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    Re: Washer Method example question (please help!!)

    It happens. Don't worry about it.

    -Dan
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