# Integration of a function.

1. Nov 12, 2008

### stanford1463

1. The problem statement, all variables and given/known data
Hey guys, I have one question: how can I integrate the function f(x,y,z)=x + y + z over the region between the paraboloid 4-x^2-y^2 and the xy-plane?

2. Relevant equations
For the paraboloid region, I used polar coordinates and found the volume of the region to be 8pi. Now, I have to find the integration of the other function x+y+z in this.

3. The attempt at a solution
Alright, I tried using a triple integral to no avail (rcos($$\theta$$) +rsin(theta) +z)r drd(theta) dz. I do not know the limits of integration (hardest part of the problem for me). Is there anyway to solve this with only a double integral? Or would I have to use cylindrical/polar whatever triple integration to solve it? Thanks..!

2. Nov 12, 2008

### HallsofIvy

Staff Emeritus
How could you find the volume if you don't know the limits of integration? If it was because you integrated
$$\int\int (4- x^2- y^2) dA= \int\int (4- r^2) r dr d\theta[/itex] then you should be able to see that is the same as [tex]\int\int\int_0^{4-x^2-y} dz dA= \int\int\int_0^{4- r^2} r dzdrd\theta$$

3. Nov 12, 2008

### stanford1463

ohh....but how is the triple integral from 0 to 4-x^2-y^2 ? I know it's the function, but graphically, I don't understand. Oh well, my homework was due 10 minutes ago and I just turned it in (leaving this question blank) lol. Thanks for the answer though!