Given two points and a radius I need to find the center of a circle. Two different circles could exist. I know that I can solve this using...

   (x-a)^2 + (y-b)^2 = r^2
   (x-A)^2 + (y-B)^2 = r^2  

...where a,b and A,B are the two points and r is the radius. Then subtract one from the other. I can do this on paper but don't know how to do it with vfp.
Any tips?