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Homework Help: Multi-d calc

  1. Apr 2, 2006 #1
    A lamina occupies the part of the disk [tex]x^2+y^2=<25[/tex] in the first quadrant and the density at each point is given by the function [tex] \ro (x,y)=3(x^2+y^2)[/tex]

    i am to find the mass, so this is what i did:

    [tex]\int _0 ^{ \frac{\pi}{ 2}} \int _0 ^{5}(3 r) r dr d \theta[/tex]

    i evauated this and got pi/2 15^3... but this is wrong, not sure why
  2. jcsd
  3. Apr 2, 2006 #2
    You should actually get [tex]\frac{125\pi}{2}[/tex] from that integral. Also,
    [tex](x^2+y^2)= r^2[/tex], not [tex]r[/tex]
    Last edited: Apr 2, 2006
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