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Math Help - volume by cylinderical shells

  1. #1
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    volume by cylinderical shells

    Find the volume of the region bound by y=x^2 and y=x+2 revolved over the x-axis from -1 to 2 using the shell method

    i tried dividing up the function into -sqrt(y) and sqrt(y) and x = y-2 but every time i try calculating the volume, i keep on getting the wrong answer, i know that the right answer is 14.4pi from the washer method. can anyone help me with this?

    thanks alot
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  2. #2
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    Re: volume by cylinderical shells

    It is hard to say what you did wrong when you don't say what you did! I note that the "cylindrical shells", rotated about the x-axis, so radius y, will have "height" given by \sqrt{y}- (y- 2) for y between 1 and 2 and by \sqrt{y}- 0 for y between 0 and 1. Did you take that into account?
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