Title: Determine The circumcenter of 3 points?
procedure Circumcenter(const x1, y1, x2, y2, x3, y3: Double; out Px, Py: Double);
var
A: Double;
C: Double;
B: Double;
D: Double;
E: Double;
F: Double;
G: Double;
begin
A := x2 - x1;
B := y2 - y1;
C := x3 - x1;
D := y3 - y1;
E := A * (x1 + x2) + B * (y1 + y2);
F := C * (x1 + x3) + D * (y1 + y3);
G := 2.0 * (A * (y3 - y2) - B * (x3 - x2));
if IsEqual(G, 0.0) then Exit;
Px := (D * E - B * F) / G;
Py := (A * F - C * E) / G;
end;
(* End of Circumcenter *)