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**1. Homework Statement**

This is a bit hard to describe without a decent picture (or a decent brain) but try to bare with me.

Picture below shows two spheres, if the origin is at centre of A, and a line d joins the centre of the two spheres, how do I describe the position of a point r from each sphere in spherical coordinates?

------------------r---------

A

------O---------------------

-----------------------------

-------------------O--------

B

**2. Homework Equations**

Polar coordinates are in terms of r and Ø

The point r described from the origin (at A) is given by (r

_{A},Ø

_{A}), where r is line from origin to point r.

**3. The Attempt at a Solution**

If origin was at B it would have coordinates (r

_{B},Ø

_{B}) need to write these in terms of r

_{A}and Ø

_{A}.

I think r

_{B}=r

_{A}+d and Ø=Ø

_{B}-Ø

_{A}