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Math Help - Solid Of Revolution

  1. #1
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    Solid Of Revolution

    Hello all.

    Region bounded by...
    y= x^2 + 1
    y = -3x + 5
    between x = 0 and x = 1
    when rotated around x = 8

    I got a wierd answer like -100, I know this is wrong and I'm confused.
    my calculator equation was 2(Pi)fnInt((8-x)(x^2+1+3x-5),x,0,1)dx

    Any help is very appreciated
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  2. #2
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    Why does this part make sense to you?

    (x^2+1+3x-5)

    You're upside down. (Note: This is a common diagnosis when the sign is wrong but the magnitude is good.)

    Try: (5-3x)-(x^2+1)

    It's much more difficult with washers or disks. Give it a try!
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  3. #3
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    That would do it. Thanks for the help. +1
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  4. #4
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    Did you do the Washers? It's fun!
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