Standard equation of a circle with center at (h,k) is: (x-h)2 + (y-k)2 = r2
Our center is at (c,0) so our circle may be written as: (x-c)2 + (y-0)2 = r2
If the circle passes through (0,a) we have: (0-c)2 + (a-0)2 = r2
If the circle passes through (b,h) we have: (b-c)2 + (h-0)2 = r2
Which leads to: (0-c)2 + (a-0)2 = (b-c)2 + (h-0)2
Simplifying and solving for c we get: c = (b2 + h2 - a2)/2b
