Kieth, let me rephrase what I think you are asking and you tell me if it's correct. The 36" dimension represents a chord of a circle (i.e. a line connecting two points on a circle) and the 6" dimension is the distance from the chord to the edge of the circle at the midpoint of the chord. If that is what you want, the formula is: R = (1/2)x(((CxC)/(4xh))+h). R = radius C = chord length h = arc height x = multiplication, eg. c x c = c squared / = division () = order of evaluation
So in your case: R = (1/2)x(((36x36)/(4x6))+6) = .5 x ((1296/24) + 6) = .5 x (54 + 6) = .5 x 60 = 30".
Forumulas sure look ugly when you have to type them out, but there it is.