Calculating Mass of lamina in the First Quadrant

[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

 

[neutrino]

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