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Math Help - Volume problem

  1. #1
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    Unhappy Volume problem

    A rectangle with vertices (0,0), (4,0), (4,6) and (0,6) is revolved about the x-axis to create a cylinder. What is the volume of this cylinder?
    A. 32pi
    B. 96pi
    C. 144pi
    D.288pi
    E.NOTA (none of these above)

    I'm thingking of NOTA. But it confuses me at the part where it says "revolved about the x-axis", i don't know if the way I understand it is correct, because if it's not then I definitely solved it wrong :P
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  2. #2
    MHF Contributor FernandoRevilla's Avatar
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    The solution is:

    V=\pi r^2h=\pi \cdot 6^2\cdot 4=144\pi.

    Regards.

    Fernando Revilla
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  3. #3
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    pickslides's Avatar
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    I like this answer

    Quote Originally Posted by nhunhu9 View Post
    C. 144pi
    Taking a rectangle and revolving it around the x-axis certainly creates a cylinder.

    Step 1. Draw the rectangle

    Step 2. Draw the cylinder

    Then using V = \pi r^2h with r=6, h = 4 \implies V = \pi\times 6^2\times 4  = 144\pi
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  4. #4
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    Thank you. I have another question, it sounds silly , but how to you know the radius is 6? I picture how a rectangle revolves around the x axis, and 6 looks like the circumference to me. Can you please explain?
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