Hi all, I am currently thinking about an interesting geometry problem: Give N point (xi,yi) find a circle that it eclose at least 3 points and its radius is minium as possible. Print the result exactly 5 digits after the dot. I can solve the easy version of it with the limits 3<=N<=1000 and -30000<=xi,yi<=30000: http://vn.spoj.com/problems/TRIPOD/ But wth the hard version 3<=N<=100000 and -2100000000<=xi,yi<=2100000000: http://vn.spoj.com/problems/TRIPOD2/ I have no idea, can anyone show me the way to solve it?