# Homework Help: Green's Theorem not working in this problem HELP

1. Jul 21, 2008

### unilquer

I have a problem from line integrals.
My question is attached as a jpeg.
Green's theorem is not valid for mine and i couldnot find a way.
Pls take care of it.

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2. Jul 21, 2008

### rootX

3. Jul 21, 2008

### Defennder

What does the last sentence mean?

4. Jul 22, 2008

### unilquer

It is just a clue. It goes on with saying this kind of functions can be created without much effort and asks how they are written.
And unfortunately i don't have much idea how to approach the problem.

5. Jul 22, 2008

### Defennder

I would say that the hint given is a big one indeed. It would save you a lot of computational effort if you understood it correctly. Have you learnt about potential functions and conservative vector fields yet?

6. Jul 22, 2008

### unilquer

Actually, i predicted that but could not be sure. Than the answer is 0 since this is a conservative field and surface is a complete circle right?

7. Jul 22, 2008

### HallsofIvy

Since Green's theorem does not work here, then you need to directly integrate around the circle. What parameterization can you use for a circle about the origin with radius r?

8. Jul 22, 2008

### Defennder

Yep, that should be it. Although it's more correct to say it's a line integral over a closed curve.