# Homework Help: Divergence theorem

1. Jul 19, 2011

### athrun200

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

2. Relevant equations

3. The attempt at a solution
I can get the answer after applying divergence theorem to have a volume integral.

It seems the 4 points given can't form a surface.

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2. Jul 19, 2011

### Office_Shredder

Staff Emeritus
Don't confuse a surface with a plane. The surface of the cube is all six of its sides

3. Jul 19, 2011

### LCKurtz

Those four points don't form a cube either. The problem doesn't imply that they do either. But the problem says a cube includes those four vertices, and that is enough to determine the cube. Presumably you knew that otherwise how did you apply the divergence theorem? It's the surface of that cube you need to use.

4. Jul 19, 2011

### HallsofIvy

I don't believe that Office Shredder meant to imply that it was a cube- he was only giving that as an example. His point was what you said- that every solid has a surface (not necessarily smooth) as boundary. Here, the surface is made of four planes.

5. Jul 19, 2011

### LCKurtz

If you are addressing that to me, I was neither quoting nor replying to Office Shredder. The original post clearly refers to the cube containing those four vertices, not a tetrahedron, and the OP was apparently missing that when trying to figure out the surface.

6. Jul 19, 2011

### hunt_mat

Well, you know that a cube has 6 sides that are the same, so from the the information given you should be able to construct the cube from that.