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<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 n/10000.0;
}

double solvex(){
	double k,l;
	k = (c*c)-(a*a)+(d*d)-(b*b)-(2*y*(d-b));
	l = 2*(c-a);
	return k/l;
}

double solvey(){
	double k,l;
	k = ((e-a)*((c*c)-(a*a)+(d*d)-(b*b)))-((c-a)*((e*e)-(a*a)+(f*f)-(b*b)));
	l = 2*(((d-b)*(e-a))-((f-b)*(c-a)));
	return k/l;
}

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

C++: #include<complex>
#include<stdio.h>
#define F(a,b,c) acos((b*b+c*c-a*a)/2/b/c)
int main(){typedef double D;int n;D d,e,f,g,h,i;for(scanf("%d",&n);n--;){scanf("%lf%lf%lf%lf%lf%lf",&d,&g,&e,&h,&f,&i);std::complex<D> a(d,g),b(e,h),c(f,i);float A=abs(b-c),B=abs(c-a),C=abs(a-b),L=F(A,B,C),s=sin(2*L),t=sin(2*F(B,C,A)),u=sin(2*F(C,A,B)),v=s+t+u;printf("%.3f %.3f %.3f\n",(d*s+e*t+f*u)/v,(g*s+h*t+i*u)/v,A/sin(L)/2);}}

C++: #include<complex>
#include<cstdio>
#include<cmath>
using namespace std;
typedef complex<double> P;
double F(double a,double b,double c){
	return acos((b*b+c*c-a*a)/(2*b*c));
}
int main(){
	int n;
	double d,e,f,g,h,i;
	for(scanf("%d",&n);n--;){
		scanf("%lf%lf%lf%lf%lf%lf",&d,&g,&e,&h,&f,&i);
		P a(d,g),b(e,h),c(f,i);
		double A=abs(b-c),B=abs(c-a),C=abs(a-b),
		s=sin(2*F(A,B,C)),t=sin(2*F(B,C,A)),u=sin(2*F(C,A,B)),v=s+t+u;
		printf("%.3f %.3f %.3f\n",(d*s+e*t+f*u)/v,(g*s+h*t+i*u)/v,A/sin(F(A,B,C))/2);
	}
}

C++: #include<iostream>
#include<iomanip>
#include<cmath>
using namespace std;

int main ()
{
    int num;
    double x1,y1,x2,y2,x3,y3;

    cin >> num;

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

        px = ((x1*x1-x3*x3+y1*y1-y3*y3)*(y2-y1)-(x1*x1-x2*x2+y1*y1-y2*y2)*(y3-y1)) / (2*(x2-x1)*(y3-y1)-2*(x3-x1)*(y2-y1));
        py = ((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));
        //py = ((2*(x1-x2)*px+x2*x2-x1*x1+y2*y2-y1*y1)) / (2*(y2-y1));
        r = sqrt((px-x1)*(px-x1) + (py-y1)*(py-y1));

        cout << fixed;
        cout << setprecision(3) << px << " " << py << " " << r << endl;
    }

    return 0;
}