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Math Help - Help on a rather easy volume problem

  1. #1
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    Help on a rather easy volume problem

    The problems is to find the volume of the genrated solid when rotated about the y-axis:

    y=x^3 + 1 x=0 and y=2

    Here is the thing though. I did this exercise using disks and got ~.5 , then I checked the answer in the back and was different, then I used shells and got the right answer. However, I've been going back to the disk method and cannot seems to find my error and keep getting the same asnwer.
    Anyone want to see if they get ~1.88 using the disks method.
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  2. #2
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    Quote Originally Posted by Arturo_026 View Post
    The problems is to find the volume of the genrated solid when rotated about the y-axis:

    y=x^3 + 1 x=0 and y=2

    Here is the thing though. I did this exercise using disks and got ~.5 , then I checked the answer in the back and was different, then I used shells and got the right answer. However, I've been going back to the disk method and cannot seems to find my error and keep getting the same asnwer.
    Anyone want to see if they get ~1.88 using the disks method.

    y=x^3+1\Longleftrightarrow x=\sqrt[3]{y-1}\Longrightarrow evaluate \pi\!\!\int\limits_1^2(x-1)^{2\slash 3}dx=\frac{3\pi}{5}\approx 1.8849556

    Tonio
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  3. #3
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    Quote Originally Posted by tonio View Post
    y=x^3+1\Longleftrightarrow x=\sqrt[3]{y-1}\Longrightarrow evaluate \pi\!\!\int\limits_1^2(x-1)^{2\slash 3}dx=\frac{3\pi}{5}\approx 1.8849556

    Tonio
    Amazing, I just realize that I was solving the problem using the equations of the problem just above it.
    Thanks for your time.
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