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++: #include <iostream>
#include <iomanip>
#include <math.h>

using namespace std;

int main(){
    int cnt;
    cin >> cnt;
    double x1, y1, x2, y2, x3, y3;
    double a1, a2, b1, b2, c1, c2;
    double a, b, c;
    double A;
    double xp, yp, r;
    while(cnt > 0 && cin >> x1 >> y1 >> x2 >> y2 >> x3 >> y3) {
        // ?????\??????????????§?¨?????±???????
        a1 = 2 * (x2 - x1);
        b1 = 2 * (y2 - y1);
        c1 = x1 * x1 - x2 * x2 + y1 * y1 - y2 * y2;
        a2 = 2 * (x3 - x1);
        b2 = 2 * (y3 - y1);
        c2 = x1 * x1 - x3 * x3 + y1 * y1 - y3 * y3;
        xp = (double)((b1*c2 - b2*c1)/(a1*b2 - a2*b1)*1000) / 1000.0;
        yp = (double)((c1*a2 - c2*a1)/(a1*b2 - a2*b1)*1000) / 1000.0;

     r=hypot(xp-x1,yp-y1);

        cout << fixed << setprecision(3);
        cout << xp << " " << yp << " " << r << endl;
        cnt -= 1;
    }
    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 = cen2.real() >= 0 ? 1000*cen2.real()+0.5 : 1000*cen2.real()-0.5;
		int y1000 = cen2.imag() >= 0 ? 1000*cen2.real()+0.5 : 1000*cen2.real()-0.5;
		int r1000 = r2          >= 0 ? 1000*r2         +0.5 : 1000*r2         -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<cmath>
#include<cstdio>

double a,b,c,d,e,f,x,y,r;
int n;

double ifof(double a){
	int n = a*10000;
	if(n%10 >= 5)
		n++;
	return (double)n/10000.0;
}

double middle(double m, double n, double o){
	using std::max;
	using std::min;
	return (max(m,max(n,o))+min(m,min(n,o)))/2;
}

int main(){
	std::cin >> n;
	for(int i=0; i<n; i++){
		std::cin >> a >> b >> c >> d >> e >> f;
		x = middle(a,c,e);
		y = middle(b,d,f);
		r = std::sqrt(((x-a)*(x-a)) + ((y-b)*(y-b)));
		std::printf("%.3f %.3f %.3f\n",ifof(x),ifof(y),ifof(r));
	}
	return 0;
}

C++: #include<stdio.h>
#include<math.h>
int main(){
	int a;
	scanf("%d",&a);
	while(a--){
		double x1,y1,x2,y2,x3,y3;
		scanf("%lf%lf%lf%lf%lf%lf",&x1,&y1,&x2,&y2,&x3,&y3);
		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 x=(b1*c2-b2*c1)/(a1*b2-a2*b1);
		double y=(c1*a2-c2*a1)/(a1*b2-a2*b1);
		double r=hypot(x-x1,y-y1);
		printf("%.3lf %.3lf %.3lf\n",x,y,r);
	}
}

C++: #include<bits/stdc++.h>
#define rep(i,n)for(int i=0;i<(n);i++)
using namespace std;

int main() {
	int n; scanf("%d", &n);
	rep(i, n) {
		double x1, y1, x2, y2, x3, y3;
		cin >> x1 >> y1 >> x2 >> y2 >> x3 >> y3;
		double a = -x1 + x2, b = -y1 + y2, c = (-pow(x1, 2) - pow(y1, 2) + pow(x2, 2) + pow(y2, 2)) / 2;
		double d = -x2 + x3, e = -y2 + y3, f = (-pow(x2, 2) - pow(y2, 2) + pow(x3, 2) + pow(y3, 2)) / 2;
		double y = (c*d - a*f) / (b*d - a*e);
		double x = (c - b*y) / a;
		if (y == NAN)y = 0;
		if (x == NAN)x = 0;
		printf("%.3lf %.3lf %.3lf\n", x, y, hypot(x1 - x, y1 - y));
	}
}

C++: #include <algorithm>
#include <functional>
#include <cmath>
#include <cstdio>
#include <cstdint>
#include <cstdlib>
#include <cstring>
#include <string>
#include <sstream>
#include <iostream>
#include <iomanip>
#include <vector>
#include <list>
#include <stack>
#include <queue>
#include <map>
#include <set>
#include <bitset>
#include <climits>
#include <complex>
 
#define all(c) (c).begin(), (c).end()
#define rep(i,n) for(int i=0;i<(n);i++)
#define pb(e) push_back(e)
#define mp(a, b) make_pair(a, b)
#define fr first
#define sc second
 
const int INF=100000000;
int dx[4]={1,0,-1,0};
int dy[4]={0,1,0,-1};
using namespace std;
typedef complex<double> P;
int n;
 
double cross(P p1,P p2) {
    return (real(p1)*imag(p2) - imag(p1)*real(p2));
}
double calc_S(P p1,P p2,P p3) {
    double ret = 0.0;
    p1 -= p3;
    p2 -= p3;
 
    ret = cross(p1,p2)/2.0;
     
    return abs(ret);
}
 
int main() {
    cin>>n;
    while(n-->0) {
        double x1_,y1_;
        double x2_,y2_;
        double x3_,y3_;
        cin>>x1_>>y1_>>x2_>>y2_>>x3_>>y3_;
        P p1(x1_,y1_);
        P p2(x2_,y2_);
        P p3(x3_,y3_);
        P A = p1-p2;
        P B = p2-p3;
        P C = p1-p3;
        double S = calc_S(p1,p2,p3);
        double R = abs(A)*abs(B)*abs(C)/S;
        R /= 4.0;
         
        P A1 = 2.0*(p2-p1);
        P B1 = 2.0*(p3-p1);
        P C1 = P(norm(p1)-norm(p2),norm(p1)-norm(p3));
        double X = cross(P(imag(A1),imag(B1)),C1)/cross(A1,B1);
        double Y = cross(C1,P(real(A1),real(B1)))/cross(A1,B1);
        printf("%.3lf %.3lf %.3lf\n",X,Y,R);
 
    }
    return 0;
}

C++: #include <iostream>
#include <cmath>
#include <iomanip>
using namespace std;
 
int main(void)
{
    int n;
    double x1, x2, x3, y1, y2, y3;
    cin >> n;
    while (cin >> x1 >> y1 >> x2 >> y2 >> x3 >> y3) {
        double a = 2 * (x1 - x2);
        double b = 2 * (y1 - y2);
        double c = x1*x1 - x2*x2 + y1*y1 - y2*y2;
        double d = 2 * (x1 - x3);
        double e = 2 * (y1 - y3);
        double f = x1*x1 - x3*x3 + y1*y1 - y3*y3;
        double p1 = (e * c - b * f) / (e * a - b * d);
        double p2 = (d * c - a * f) / (d * b - a * e);
        double r = sqrt(pow(x1 - p1, 2) + pow(y1 - p2, 2));
        cout << fixed << std::setprecision(10);
        cout << p1 << " " << p2 << " " << r;
    }
    return 0;
}

C++: #include <iomanip>
#include <iostream>
#include "math.h"
using namespace std;

/** Problem0010 : CIrcumscribed Circle of a Triangle **/
int main()
{
	int n;
	double X1, Y1, X2, Y2, X3, Y3;
	double a, b, c, d, e, f, l, m;
	cin >> n;
	for (int i=0; i<n; i++) {
		cin >> X1 >> Y1 >> X2 >> Y2 >> X3 >> Y3;
		a = X1-X2; b = Y1-Y2; c = -(X1*X1+Y1*Y1)+(X2*X2+Y2*Y2);
		d = X2-X3; e = Y2-Y3; f = -(X2*X2+Y2*Y2)+(X3*X3+Y3*Y3);
		l = (c*e - b*f)/(e*a - b*d); m = (c*d - a*f)/(b*d - a*e);
		cout << setprecision(3) << setiosflags(ios::fixed);
		cout << -l/2 << " " << -m/2 << " " << sqrt(l*l+m*m-4*n)/2 << endl;
	}
	return 0;
}