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Homework Help: Integrating in polar coordinates (volume)

  1. Mar 28, 2009 #1
    1. The problem statement, all variables and given/known data

    The solid bounded by the parabolids z = 3x^2 + 3y^2 -7 and z = -x^2 -y^2 + 9

    2. Relevant equations

    3. The attempt at a solution

    Ok so i set the two z equations into polar form and came up with 3r^2 = 7 and r^2 = 9
    I thought that r went from (7/3) ^(1/2) to 3 and that theta went from 0 to 2pi.
    I figured the equation to integrate was -4r^2 + 16. (Outer bounds -inner bounds) Anyway, the answer the book gives is different than the two different ways I tried. Just need help setting up the integral...thanks
  2. jcsd
  3. Mar 28, 2009 #2
    This is a 3-D problem; you were given z coordinate values in each case. Work with those.
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