三角形外接圆圆心

Point  circle_center(Point  pt[3]) 
{ 
           double  x1,x2,x3,y1,y2,y3; 
           double  x  =  0; 
           double  y  =  0; 

           x1  =  pt[0].x; 
           x2  =  pt[1].x; 
           x3  =  pt[2].x; 
           y1  =  pt[0].y; 
           y2  =  pt[1].y; 
           y3  =  pt[2].y; 

           x=((y2-y1)*(y3*y3-y1*y1+x3*x3-x1*x1)-(y3-y1)*(y2*y2-y1*y1+x2*x2-x1*x1))/(2*(x3-x1)*(y2-y1)-2*((x2-x1)*(y3-y1)));
            y=((x2-x1)*(x3*x3-x1*x1+y3*y3-y1*y1)-(x3-x1)*(x2*x2-x1*x1+y2*y2-y1*y1))/(2*(y3-y1)*(x2-x1)-2*((y2-y1)*(x3-x1)));
           Point center;
           center.x  =  x  ; 
           center.y  =  y  ; 
           return center;
}