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Volume of Solids of revolution help.

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  • 04-01-2012 7:17pm
    #1
    Iancar29
    Registered Users Posts: 5,068 ✭✭✭


    Hi folks , if anyone could help me out here would much appreciate it.


    Ok im doing the volume of solid of revolution.

    I think i know how to get the answer for one graph say:

    Y = 1/8 x^3 ( about y axis. )

    I go V = Int a-b (pi) ( 1/8 x^3 ) dy

    Gettin an ans =16 (pi)

    But when 2 graphs are given , the 2nd being : y = 2x . DO i just do the same with that ( ans = 1 pi ) and just subtract the 2? The Q says the graphs are bounded , hence i found the intersections of a-b = 1-4 .

    Cant find examples regarding involving 2 graphs
    Thanks in advance :)


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    #2
    TheBody
    Registered Users Posts: 5,619 ✭✭✭TheBody


    Iancar29 wrote: »
    Hi folks , if anyone could help me out here would much appreciate it.


    Ok im doing the volume of solid of revolution.

    I think i know how to get the answer for one graph say:

    Y = 1/8 x^3 ( about y axis. )

    I go V = Int a-b (pi) ( 1/8 x^3 ) dy

    Gettin an ans =16 (pi)

    But when 2 graphs are given , the 2nd being : y = 2x . DO i just do the same with that ( ans = 1 pi ) and just subtract the 2? The Q says the graphs are bounded , hence i found the intersections of a-b = 1-4 .

    Cant find examples regarding involving 2 graphs
    Thanks in advance :)

    Check this video out and see if that helps you.

    http://www.youtube.com/watch?v=E5OOMbz5jZk

    We'll help you out if you are still stuck.


  • Options
    #3
    Iancar29
    Registered Users Posts: 5,068 ✭✭✭Iancar29


    TheBody wrote: »
    Check this video out and see if that helps you.

    http://www.youtube.com/watch?v=E5OOMbz5jZk

    We'll help you out if you are still stuck.

    Cheers thanks! ... the question being rotated around the y-axis doesnt make a difference in the " first line i hit " ... as if it was the other way around the volume would be negative.

    Got a nice clean answer of 6.1 (pi) .

    Thank you.


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