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Math Help - More volume of graphs

  1. #1
    Member >_<SHY_GUY>_<'s Avatar
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    More volume of graphs

    from the graph 2x + y = 2, a solid is generated by revolving it about the x-axis. here is the graph with the endpoints

    For my answer, i got pi/3 is that correct?
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  2. #2
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    That's not what I got. Can you show us how you set up the integral?
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  3. #3
    Member >_<SHY_GUY>_<'s Avatar
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    Quote Originally Posted by drumist View Post
    That's not what I got. Can you show us how you set up the integral?
    i set up my integral in terns of x

    i dont know how to use the integral sign here, so excuse me as i try to explain it.

    the integral pi/3 times the integral of -2x+2 dx from 2 to 1 [i have a feeling thats wrong]
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  4. #4
    Junior Member eddie2042's Avatar
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    Quote Originally Posted by >_<SHY_GUY>_< View Post
    from the graph 2x + y = 2, a solid is generated by revolving it about the x-axis. here is the graph with the endpoints

    For my answer, i got pi/3 is that correct?
    Just use the method of disks

    V = \pi\int_0^1(-2x + 2)^2 dx
    V = \pi\int_0^1(4x^2 - 8x + 4)dx
    V = \pi\left[\frac{4x^3}{3} - 4x^2 + 4x\right]_0^1
    V = \frac{4\pi}{3}
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  5. #5
    Member >_<SHY_GUY>_<'s Avatar
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    Quote Originally Posted by eddie2042 View Post
    Just use the method of disks

    V = \pi\int_0^1(-2x + 2)^2 dx
    V = \pi\int_0^1(4x^2 - 8x + 4)dx
    V = \pi\left[\frac{4x^3}{3} - 4x^2 + 4x\right]_0^1
    V = \frac{4\pi}{3}
    how do you know when to use disk? how is the way i approached the problem wrong? Im just really curious as to how to determine it

    thank you so much
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