Dirac Delta in polar coordinates

[johnsmi]

Homework Statement

Hi, I would like to know what is the right way to write continuous deltas standing in a circle of radius a?

Homework Equations

The Attempt at a Solution

I am not sure weather it's δ(r-a) or is it
δ(r-a)/|r-a|
Thank you

 

[hunt_mat]

You know that:
$$f(x,y)=\int_{-\infty}^{\infty}f(u,v)\delta (x-u)\delta (y-v)dxdy$$
Now make a change of co-ordinates from Cartesian to polar, and the answer should drop out for you. Failing that look it up on Wikipedia )

Mat