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Homework Help: Solid of revolution problem

  1. Sep 18, 2011 #1
    1. The problem statement, all variables and given/known data

    rotated around y
    2. Relevant equations
    integral 2pi*x(f(x)dx

    3. The attempt at a solution

    integral from -6 to 6 of 2pi*y*2y^2 dy
    but i get something far less than the correct answer
  2. jcsd
  3. Sep 18, 2011 #2
    What are all the * symbols supposed to mean? Multiplication?

    Just think of this as Area times length. Since it's rotation around the y axis you can see that it's easiest to differentiate with respect to y. It's going to make a bunch of little circles. What is the radius of those? (your function?).

    From there, you need to plug it into the area of a circle to get pi(radius)^2
    So if the volume of the solid is area times width, and in the integration dy is the width, what integral would solve this problem?
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