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Math Help - Disk method.

  1. #1
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    Disk method.

    find the volume of the solid generated by revolving each region about the y-axis

    the region in the first quadrant bounded above by the parabola y=x^2, below by the x, axis, and on the right by the line x=2.

    Worked this problem out like 5 times idk why i cant get the right answer. cannot find what im doing wrong. It seems pretty simple. Answers 8Pi. HELP PLZ
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  2. #2
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    Quote Originally Posted by jeffjohnson View Post
    find the volume of the solid generated by revolving each region about the y-axis

    the region in the first quadrant bounded above by the parabola y=x^2, below by the x, axis, and on the right by the line x=2.

    Worked this problem out like 5 times idk why i cant get the right answer. cannot find what im doing wrong. It seems pretty simple. Answers 8Pi. HELP PLZ
    washers ...

    R = 2

    r = \sqrt{y}

    V = \pi \int_0^4 2^2 - (\sqrt{y})^2 \, dy<br />

    work it out ...
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    Quote Originally Posted by jeffjohnson View Post
    find the volume of the solid generated by revolving each region about the y-axis

    the region in the first quadrant bounded above by the parabola y=x^2, below by the x, axis, and on the right by the line x=2.

    Worked this problem out like 5 times idk why i cant get the right answer. cannot find what im doing wrong. It seems pretty simple. Answers 8Pi. HELP PLZ
    Hi jeff,

    using the integral of cylindrical surface areas,

    \int_{0}^22{\pi}\left((x)x^2\right)dx=2{\pi}\left(  \frac{2^4}{4}\right)=\frac{2^5{\pi}}{4}
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