private void GetTriangleExcenterRadius(Point A, Point B, Point C, out double R, out Point center)

        {

            //same point

            if (A == B && A == C)

            {

                R = ;

                center = A;

                return;

            }

            double x1 = A.X, x2 = B.X, x3 = C.X, y1 = A.Y, y2 = B.Y, y3 = C.Y;

            double C1 = Math.Pow(x1, ) + Math.Pow(y1, ) - Math.Pow(x2, ) - Math.Pow(y2, );

            double C2 = Math.Pow(x2, ) + Math.Pow(y2, ) - Math.Pow(x3, ) - Math.Pow(y3, );

            double centery = (C1 * (x2 - x3) - C2 * (x1 - x2)) / ( * (y1 - y2) * (x2 - x3) -  * (y2 - y3) * (x1 - x2));

            double centerx = (C1 -  * centery * (y1 - y2)) / ( * (x1 - x2));

            center = new Point(centerx, centery);

            R = GetDistance(A, center);

        }

private double GetDistance(Point A, Point B)

        {

            return Math.Sqrt(Math.Pow((A.X - B.X), ) + Math.Pow((A.Y - B.Y), ));

        }