1. Limited time only! Sign up for a free 30min personal tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Homework Help: What am I doing wrong with this integral?

  1. Apr 14, 2009 #1
    1. The problem statement, all variables and given/known data

    2. Relevant equations

    [tex]\int_{-1}^3 \int_0^{3y} (x^2+y^2) dxdy[/tex]

    3. The attempt at a solution

    I've gotten [tex] \int_{-1}^3 \frac{x^3}{3}[/tex] = [tex] \int_{-1}^{3}y^3 dy[/tex] for the first part, but this can't be right?
  2. jcsd
  3. Apr 14, 2009 #2
    How are you getting that equals sign in there?
    Aren't you solving:
    [tex]\int_{-1}^3 \int_0^{3y} (x^2+y^2) dxdy[/tex] = ?

    Try splitting it up to help you see it more easily, maybe:
    [tex]\int_{-1}^3 \int_0^{3y}x^2dxdy+\int_{-1}^3 \int_0^{3y}y^2dxdy[/tex] = ?
  4. Apr 14, 2009 #3
    For the first integral I get:

    [tex] \int_{-1}^3 y^3 dy[/tex]
    Is that right so far?
  5. Apr 14, 2009 #4
    Well, no... because you know:

    [tex]\int_{-1}^3 \int_0^{3y}x^2dxdy=\int_{-1}^3 \frac{(3y)^3}{3}dy[/tex]
  6. Apr 14, 2009 #5
    Oh. Oops. :)
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook