1 #include <iostream> 2 #include<cstdio> 3 #include<cstring> 4 #include<algorithm> 5 #include<stdlib.h> 6 #include<vector> 7 #include<cmath> 8 #include<queue> 9 #include<set>10 using namespace std;11 #define N 10000012 #define LL long long13 #define INF 0xfffffff14 const double eps = 1e-8;15 const double pi = acos(-1.0);16 const double inf = ~0u>>2;17 struct Point18 {19     double x,y;20     Point (double x=0,double y =0):x(x),y(y){}21 }p[4];22 struct Circle23 {24     Point center;25     double r;26 };27 typedef Point pointt;28 pointt operator - (Point a,Point b)29 {30     return Point(a.x-b.x,a.y-b.y);31 }32 int dcmp(double x)33 {34     if(fabs(x)<eps) return 0;35     return x<0?-1:1;36 }37 double dis(Point a)38 {39     return a.x*a.x+a.y*a.y;40 }41 double cross(Point a,Point b)42 {43     return a.x*b.y-a.y*b.x;44 }45 double area()46 {47     return fabs(cross(p[1]-p[2],p[2]-p[3]))/2;48 }49 struct Circle Circumcircle()50 {51     Circle tmp;52     double a,b,c,c1,c2;53     double xa,ya,xb,yb,xc,yc;54     a = sqrt(dis(p[3]-p[1]));55     b = sqrt(dis(p[1]-p[2]));56     c = sqrt(dis(p[2]-p[3]));57     //根据s = a*b*c/R/4，求半径58     tmp.r = (a*b*c)/(area()*4.0);59     xa = p[3].x;60     ya = p[3].y;61     xb = p[1].x;62     yb = p[1].y;63     xc = p[2].x;64     yc = p[2].y;65     c1 = (dis(p[3])-dis(p[1]))/2;66     c2 = (dis(p[3])-dis(p[2]))/2;67     tmp.center.x = (c1*(ya-yc)-c2*(ya-yb))/((xa-xb)*(ya-yc)-(xa-xc)*(ya-yb));68     tmp.center.y = (c1*(xa-xc)-c2*(xa-xb))/((ya-yb)*(xa-xc)-(ya-yc)*(xa-xb));69     return tmp;70 }71 int main()72 {73     while(scanf("%lf%lf%lf%lf%lf%lf",&p[1].x,&p[1].y,&p[2].x,&p[2].y,&p[3].x,&p[3].y)!=EOF)74     {75         Circle cc = Circumcircle();76         double r = cc.r;77         char c1,c2;78         c1 = dcmp(cc.center.x)>0?‘-‘:‘+‘;79         c2 = dcmp(cc.center.y)>0?‘-‘:‘+‘;80         printf("(x %c %.3f)^2 + (y %c %.3f)^2 = %.3f^2\n",c1,fabs(cc.center.x),c2,fabs(cc.center.y),r);81         double s = r*r-cc.center.x*cc.center.x-cc.center.y*cc.center.y;82         char c3 = dcmp(s)>0?‘-‘:‘+‘;83         printf("x^2 + y^2 %c %.3fx %c %.3fy %c %.3f = 0\n",c1,fabs(cc.center.x*2),c2,fabs(cc.center.y*2),c3,fabs(s));84         puts("");85     }86     return 0;87 }