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Volume radius problem

  1. Dec 29, 2005 #1
    The volume surrounded by y = x^2 , y=0, x=-2, x=-1 , revolved about y axis,by using cylindrical method.

    The region is actually within x=-1 to -2 and it can actually same with x=1 to 2.

    radius = 2-x
    height = x^2

    Is my assumption correct?
  2. jcsd
  3. Dec 29, 2005 #2


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    Your radius should simply be x. With limits of: x = 1 to 2

    You assumption about being able to use the region in the 1st quadrant is correct, yes.
  4. Dec 29, 2005 #3
    How come the radius should be x?
  5. Dec 29, 2005 #4


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    The radius should be x because the radius of the cylinder is the distance from the origin.
    The volume of revolution is about the y-axis, which passes through the origin. And you are finding the volumes of all the thin cylinders starting with cylinders with a radius of x = 1 to x= 2.

    See here for a further treatment of the cylindrical method.
    Last edited: Dec 30, 2005
  6. Dec 30, 2005 #5
    Something wrong with the link you have given.
  7. Dec 30, 2005 #6


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    Sorry 'bout that. Forgot to add in the url.
    The link is fixed now.
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