# Homework Help: Surface Integral

1. Feb 24, 2010

### bon

1. The problem statement, all variables and given/known data

So trying to find the Integral of A.n dS where A is (y,2x,-z) and S is the surface of the plane 2x+y = 6 in the first octant cut off by the plane z=4

2. Relevant equations

3. The attempt at a solution

So i always solve these by projection...but im a bit confused this time..

normally the surface is in the form z=f(x,y) so i do z-f(x,y) and take grad to find the normal..

so is the normal vector here just (2,1)? ie. grad 2x-y-6 = 0?

In which case is the integral just the double integral of (y,2x,-4).(2,1,0) dA?

Im a bit confused..Any help would be great!

2. Feb 25, 2010

### bon

Any ideas..?
I'm pretty confused about which plane you project onto to solve this...

Thanks!

3. Feb 25, 2010

### bon

So do you project onto y-z plane?

and is the integral therefore the 1/2 times the double integral of A.(2,1,0) dydz?