Go: package main

import (
	"fmt"
	"math"
)

func main() {
	var num int
	fmt.Scan(&num)
	for i := 0; i < num; i++ {
		var x1, y1, x2, y2, x3, y3 float64
		fmt.Scanf("%f%f%f%f%f%f", &x1, &y1, &x2, &y2, &x3, &y3)

		a := 2 * (x2 - x1)
		b := 2 * (y2 - y1)
		c := 2 * (x3 - x1)
		d := 2 * (y3 - y1)
		e := x2*x2 - x1*x1 + y2*y2 - y1*y1
		f := x3*x3 - x1*x1 + y3*y3 - y1*y1

		// 直線1: ax + by - e = 0
		// 直線2: cx + dy - f = 0
		px := (d*e - b*f) / (a*d - b*c)
		py := (c*e - a*f) / (b*c - a*d)
		r := math.Sqrt((px-x1)*(px-x1) + (py-y1)*(py-y1))
		fmt.Printf("%.3f %.3f %.3f\n", px, py, r)
	}
}

C++: // AOJ 0010 (http://judge.u-aizu.ac.jp/onlinejudge/description.jsp?id=0010&lang=jp)
#include<cstdio>
#include<cmath>
#define rep(i,a) for(int i=0;i<(a);++i)

int n;

double sqr( double x )
{ return x*x; }

int main()
{
	scanf( "%d", &n );
	while( n-- )
	{
		double x1, y1, x2, y2, x3, y3;
		scanf( "%lf%lf%lf%lf%lf%lf", &x1, &y1, &x2, &y2, &x3, &y3 );

		double a = sqrt(sqr(x3-x2)+sqr(y3-y2)), b = sqrt(sqr(x1-x3)+sqr(y1-y3)), c = sqrt(sqr(x2-x1)+sqr(y2-y1));
		double cosA = (sqr(b)+sqr(c)-sqr(a))/(2*b*c), cosB = (sqr(c)+sqr(a)-sqr(b))/(2*c*a), cosC = (sqr(a)+sqr(b)-sqr(c))/(2*a*b);
		double sinA = sqrt(1-sqr(cosA)), sinB = sqrt(1-sqr(cosB)), sinC = sqrt(1-sqr(cosC));
		double sin2A = 2*sinA*cosA, sin2B = 2*sinB*cosB, sin2C = 2*sinC*cosC;
		double px = (sin2A*x1+sin2B*x2+sin2C*x3)/(sin2A+sin2B+sin2C), py = (sin2A*y1+sin2B*y2+sin2C*y3)/(sin2A+sin2B+sin2C);

		printf( "%.3f %.3f %.3f\n", px, py, sqrt(sqr(x1-px)+sqr(y1-py)) );
	}

	return 0;
}

C++:     }else{
      P max = point[0];
      P min = point[0];
      if(max.real() < point[1].real())max=point[1];
      if(min.real() > point[1].real())min=point[1];
      if(max.real() < point[1].real())max=point[2];
      if(min.real() > point[1].real())min=point[2];
      ans = max + min;
      ans = (ans.real()/2,ans.imag()/2);
    }

C++: #include <iostream>
#include <stdio.h>
#include <string>
#include <math.h>
#include <algorithm>
using namespace std;
int main(){
  double x1, y1, x2, y2, x3, y3;
  double px, py;
  double r;
  double M1, mx1, my1;
  double M2, mx2, my2;
  int n;
  cin >> n;

  while(1){
    if(n == 0) break;

    cin >> x1 >> y1 >> x2 >> y2 >> x3 >> y3;

    mx1 = (x1 + x2) / 2;
    my1 = (y1 + y2) / 2;
    if(y1 - y2 == 0) M1 = 0;
    else  M1 = (-1)*(x1 - x2) / (y1 - y2);
   

    mx2 = (x2 + x3) / 2;
    my2 = (y2 + y3) / 2;
    if(y2 - y3 == 0) M2 = 0;
    else  M2 = (-1)*(x2 - x3) / (y2 -y3);
    

    if(M1 == M2){
      px = mx1;
      py = my2;
    }
    else if(M1 != M2){
      if(px == 0){
        px = 0;
      }
      else{
        px = (M1*mx1 - my1 - M2*mx2 + my2) / (M1 - M2);
        py = M1*(px - mx1) + my1;
      }
    }

    r = sqrt((x1 - px)*(x1 - px) + (y1 - py)*(y1 - py));

    printf("%.3f %.3f %.3f\n",px,py,r);
    n--;
  }
 return 0; 
}

C++: #include <iostream>
#include <stdio.h>

#define MAX 1000000

using namespace std;

int main() {
	double x1, y1, x2, y2, x3, y3;
	int n;
	cin >> n;

	for (int i = 0; i < n; i++) {
		cin >> x1 >> y1 >> x2 >> y2 >> x3 >> y3;
		double x = ((y1-y3)*(y1*y1-y2*y2+x1*x1-x2*x2)-(y1-y2)*(y1*y1-y3*y3+x1*x1-x3*x3))/(2*(y1-y3)*(x1-x2)-2*(y1-y2)*(x1-x3));
		double y = ((x1-x3)*(x1*x1-x2*x2+y1*y1-y2*y2)-(x1-x2)*(x1*x1-x3*x3+y1*y1-y3*y3))/(2*(x1-x3)*(y1-y2)-2*(x1-x2)*(y1-y3));

		printf("%.3f %.3f %.3f\n", x, y, sqrt(pow((x1 - x), 2) + pow((y1 - y), 2)));
	}
	return 0;
}

C++: #include <iostream>
#include <cstdio>
#include <complex>
#include <vector>
#include <algorithm>
using namespace std;

const double EPS = 1e-7;
typedef complex<double> P; /* _ */
struct L {                 /* üª */
	P p, q;
	L(P p, P q) : p(p), q(q) {}
};

double cross(P a, P b) { return imag(conj(a)*b); }

// ¼üaÆ¼übÌð_ðvZ·éDæÉð·»èªK{D
P crossPointLL(L a, L b){
	double A = cross(a.q-a.p, b.q-b.p);
	double B = cross(a.q-a.p, a.q-b.p);
	return b.p + B/A * (b.q-b.p);
}

// _pÆ_qÌ¼ñªüðÔ·
L pointBisector(P p, P q) {
	P cen = (p+q)*0.5;
	return L(cen, cen+(q-p)*P(0,1));
}

int main(){
	int n;
	cin>>n;
	double x1, y1, x2, y2, x3, y3;
	while(cin>>x1>>y1>>x2>>y2>>x3>>y3){
		// Cuè@
		P p1 = P(x1, y1);
		P p2 = P(x2, y2);
		P p3 = P(x3, y3);
		L l1 = pointBisector(p1, p2);
		L l2 = pointBisector(p2, p3);
		P cen = crossPointLL(l1, l2);
		double r = abs(p1-cen);

		// Êè@
		double a1 = 2*(x2-x1);
		double b1 = 2*(y2-y1);
		double c1 = x1*x1-x2*x2+y1*y1-y2*y2;
		double a2 = 2*(x3-x1);
		double b2 = 2*(y3-y1);
		double c2 = x1*x1-x3*x3+y1*y1-y3*y3;
		double cx = (b1*c2-b2*c1)/(a1*b2-a2*b1);
		double cy = (c1*a2-c2*a1)/(a1*b2-a2*b1);
		P cen2 = P(cx, cy);
		double r2 = abs(p1-cen2);

		// ÜÆß
		int x1000 = cen.real() >= 0 ? 1000*cen.real()+0.5 : 1000*cen.real()-0.5;
		int y1000 = cen.imag() >= 0 ? 1000*cen.real()+0.5 : 1000*cen.real()-0.5;
		int r1000 = r          >= 0 ? 1000*r         +0.5 : 1000*r         -0.5;
		printf("%.3f %.3f %.3f", 1.0*x1000/1000, 1.0*y1000/1000, 1.0*r1000/1000);
		cout<<endl;

	}
	return 0;
}

C++: #include<iostream>
#include<stdio.h>
#include<math.h>

using namespace std;

int main(){

    int n;
    cin >> n;
    for (int i = 0; i < n;i++)
    {
        double x1, y1, x2, y2, x3, y3;
        cin >> x1 >> y1 >> x2 >> y2 >> x3 >> y3;

        double p = ((y1 - y3)*(pow(y1, 2) - pow(y2, 2) + pow(x1, 2) - pow(x2, 2)) - (y1 - y2)*(pow(y1, 2) - pow(y3, 2) + pow(x1, 2) - pow(x3, 2))) / (2 * (y1 - y3)*(x1 - x2) - 2 * (y1 - y2)*(x1 - x3));
        double q = ((x1 - x3)*(pow(x1, 2) - pow(x2, 2) + pow(y1, 2) - pow(y2, 2)) - (x1 - x2)*(pow(x1, 2) - pow(x3, 2) + pow(y1, 2) - pow(y3, 2))) / (2 * (x1 - x3)*(y1 - y2) - 2 * (x1 - x2)*(y1 - y3));
        double r = pow((pow((x1 - p), 2) + pow((y1 - q), 2)), 0.5);

        printf("%.3f %.3f %.3f\n", p, q, r);
    }

    return 0;
}

C++: #include <stdio.h>
#include <math.h>

int main(void)
{
	float x[2][3];
	int n;
	int xa, xb, xc;
	int ya, yb, yc;
	float ans[3];
	int i, j;
	
	scanf("%d", &n);
	
	while (n){
		for (i = 0; i < 3; i++){
			for (j = 0; j < 2; j++){
				scanf("%f", &x[j][i]);
			}
		}
		
		xa = 2 * (x[0][1] - x[0][0]);
		xb = 2 * (x[1][1] - x[1][0]);
		xc = x[0][0] * x[0][0] - x[0][1] * x[0][1] + x[1][0] * x[1][0] - x[1][1] * x[1][1];
		ya = 2 * (x[0][2] - x[0][0]);
		yb = 2 * (x[1][2] - x[1][0]);
		yc = x[0][0] * x[0][0] - x[0][2] * x[0][2] + x[1][0] * x[1][0] - x[1][2] * x[1][2];
		
		ans[0] = (xb * yc - yb * xc) / (xa * yb - ya * xb);
		ans[1] = (xc * ya - yc * xa) / (xa * yb - ya * xb);
		ans[2] = sqrt((ans[0] - x[0][0]) * (ans[0] - x[0][0]) + (ans[1] - x[1][0]) * (ans[1] - x[1][0]));
		
		for (i = 0; i < 3; i++){
			if (i){
				printf(" ");
			}
			printf("%.3f", ans[i]);
			
		}
		printf("\n");
		
		n--;
	}
	
	return (0);
}