# Multi-d calc

1. Apr 2, 2006

### UrbanXrisis

A lamina occupies the part of the disk $$x^2+y^2=<25$$ in the first quadrant and the density at each point is given by the function $$\ro (x,y)=3(x^2+y^2)$$

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

$$\int _0 ^{ \frac{\pi}{ 2}} \int _0 ^{5}(3 r) r dr d \theta$$

i evauated this and got pi/2 15^3... but this is wrong, not sure why

2. Apr 2, 2006

### neutrino

You should actually get $$\frac{125\pi}{2}$$ from that integral. Also,
$$(x^2+y^2)= r^2$$, not $$r$$

Last edited: Apr 2, 2006