# What the hell is Green's third identity talking about?

1. May 3, 2005

### quasar987

Here it is on Mathworld:

http://mathworld.wolfram.com/GreensIdentities.html

On Wikipedia, it's a total carnage:

http://en.wikipedia.org/wiki/Green's_identities

In Mathworld, what are r, n and ds in cartesian coordinate?

2. May 4, 2005

### arildno

r is the positive distance from the singularity, ds is the line element, and $$\frac{\partial{u}}{\partial{n}}\equiv\nabla{u}\cdot\vec{n}$$, i.e, the component of the gradient of u along the normal to the curve.

3. May 4, 2005