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<math.h>
#include<stdio.h>
using namespace std;

typedef pair<double,double>vec;

vec operator + (vec v1,vec v2){
    return make_pair(v1.first+v2.first,v1.second+v2.second);
}

vec operator - (vec v1,vec v2){
    return make_pair(v1.first-v2.first,v1.second-v2.second);
}

vec operator * (double v,vec v2){
    return make_pair(v*v2.first,v*v2.second);
}

vec operator / (vec v1,double d){
    return make_pair(v1.first/d,v1.second/d);
}

int norm2(vec v1,vec v2){
    return (v1-v2).first*(v1-v2).first+(v1-v2).second*(v1-v2).second;
}

int main(){
    double x1,x2,x3,y1,y2,y3,n,r;
    cin>>n;
    while(n--){
        cin>>x1>>y1>>x2>>y2>>x3>>y3;
        vec A = make_pair(x1,y1);
        vec B = make_pair(x2,y2);
        vec C = make_pair(x3,y3);
        double a2,b2,c2,a,b,c,cosA,cosB,cosC,sinA,sinB,sinC,cos2A,cos2B,cos2C,sin2A,sin2B,sin2C;
        a2=norm2(B,C);
        b2=norm2(A,C);
        c2=norm2(A,B);
        a=sqrt(a2);
        b=sqrt(b2);
        c=sqrt(c2);
        cosA=(b2+c2-a2)/(2*b*c);
        cosB=(a2+c2-b2)/(2*c*a);
        cosC=(b2+a2-c2)/(2*b*a);
        sinA=sqrt(1-cosA*cosA);
        sinB=sqrt(1-cosB*cosB);
        sinC=sqrt(1-cosC*cosC);
        r=(a/sinA)/2;
        cos2A=cosA*cosA-sinA*sinA;
        cos2B=cosB*cosB-sinB*sinB;
        cos2C=cosC*cosC-sinC*sinC;
        sin2A=2*sinA*cosA;
        sin2B=2*sinB*cosB;
        sin2C=2*sinC*cosC;
        
        vec v=(sin2A*A+sin2B*B+sin2C*C )   /    (sin2A+sin2B+sin2C);
        printf("%.3f %.3f %.3f\n",v.first,v.second,r);
    }
    
}

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

using namespace std;

int main() {
    int n, x1, y1, x2, y2, x3, y3;
    cin >> n;
    for (int i = 0; i < n; ++i) {
        double a1 = 2 * (x2 - x1), a2 = 2 * (x3 - x1),
               b1 = 2 * (y2 - y1), b2 = 2 * (y3 - y1),
               c1 = x1 * x1 - x2 * x2 + y1 * y1 - y2 * y2,
               c2 = x1 * x1 - x3 * x3 + y1 * y1 - y3 * y3,
               px = (b1 * c2 - b2 * c1) / (a1 * b2 - a2 * b1),
               py = (c1 * a2 - c2 * a1) / (a1 * b2 - a2 * b1),
               r = sqrt(pow(x1 - px, 2) + pow(y1 - py, 2));
        printf("%.3f %.3f %.3f\n", px, py, r);
    }
    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 = 1000*cen2.real()+0.5;
		int y1000 = 1000*cen2.imag()+0.5;
		int r1000 = 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 <complex>
#include <vector>
#include <cstdio>
using namespace std;

const double EPS = 1e-8;
const double INF = 1e12;
typedef complex<double> P;

bool operator < (const P& a, const P& b) {
  return real(a) != real(b) ? real(a) < real(b) : imag(a) < imag(b);
}

double cross(const P& a, const P& b) {
  return imag(conj(a)*b);
}
double dot(const P& a, const P& b) {
  return real(conj(a)*b);
}
struct L : public vector<P> {
  L(const P &a, const P &b) {
    push_back(a); push_back(b);
  }
};

L caln(P a, P b) {
  return L((a+b)*P(0.5,0), (a+b)*P(0.5,0) + (b-a)*P(0, 1));
}

P intersect(L a, L b) {
  P aa(a[1]-a[0]), bb(b[1]-b[0]);
  return a[0] + aa * cross(bb, b[0]-a[0]) / cross(bb, aa);
}

int main() {
  int n;
  cin >> n;
  while(n--) {
    double x1,y1,x2,y2,x3,y3;
    cin >> x1 >> y1 >> x2 >> y2 >> x3 >> y3;
    P a1(x1,y1), a2(x2,y2), a3(x3,y3);
    P ans = intersect(caln(a1,a2), caln(a2,a3));
    printf("%.3f %.3f %.3f\n", real(ans),imag(ans),abs(a1-ans));
  }
}

C++: #include <cstdio>
#include <string>
#include <vector>
#include <algorithm>
#include <memory.h>
#include <cmath>
#include <map>
#include <set>
#include <queue>
#include <stack>
#include <ctime>
#include <iostream>
#include <functional>
#include <complex>
#include <iomanip>
#pragma comment(linker, "/STACK:836777216")

using namespace std;

typedef long long ll;
typedef pair<int, int> pii;
typedef pair<ll, ll> pll;
typedef pair<double, double> pdd;
typedef pair<pii, int> p3i;
typedef vector<int> vi;
typedef vector<pii> vii;
typedef vector<pll> vll;
typedef vector<p3i> v3i;
typedef vector<vii> vvii;
typedef vector<p3i> vp3i;
typedef long double ld;
typedef vector<ld> vld;

#define pb push_back
#define mp make_pair
#define REP(i, n) for (int (i) = 0; (i) < (n); (i)++)
#define REPD(i, n) for (int (i) = (n) - 1; (i) >= 0; (i)--)
#define FOR(i, a, b) for (int (i) = (a); (i) < (b); (i)++)
#define FORD(i,a, b) for (int (i) = (a); (i) >= (b); (i)--)
#define sz(v) (int)(v).size()
#define all(v) (v).begin(), (v).end()
#define rv(v) reverse(all(v))
#define CL(v, val) memset((v), (val), sizeof((v)))
#define SORT(a) sort(all(a))
#define un(v) SORT(v), (v).resize(unique(all(v)) - (v).begin())
#define eps 1.0e-7
#define X first
#define Y second
#define bit(n) (1 << (n))
#define bit64(n) (ll(1) << (n))
#define sqr(n) ((n) * (n))

double x[3], y[3];
double l[3];

double GetDist(int a, int b) {
  return sqrt(sqr(x[a] - x[b]) + sqr(y[a] - y[b]));
}

int main(void) {
  int n;
  scanf("%d", &n);
  REP(i, n) {
    REP(j, 3) {
      scanf("%lf%lf", &x[j], &y[j]);
    }

    double D = 2 * (x[0] * (y[1] - y[2]) + x[1] * (y[2] - y[0]) + x[2] * (y[0] - y[1]));
    double xc = 1.0 / D * ((sqr(x[0]) + sqr(y[0])) * (y[1] - y[2]) + (sqr(x[1]) + sqr(y[1])) * (y[2] - y[0]) + (sqr(x[2]) + sqr(y[2])) * (y[0] - y[1]));
    double yc = 1.0 / D * ((sqr(x[0]) + sqr(y[0])) * (x[2] - x[1]) + (sqr(x[1]) + sqr(y[1])) * (x[0] - x[2]) + (sqr(x[2]) + sqr(y[2])) * (x[1] - x[0]));

    double p = 0;
    REP(j, 3) {
      l[j] = GetDist(j, (j + 1) % 3);
      p += l[j];
    }

    p /= 2;

    double r = 1;
    double z = p;
    REP(j, 3) {
      r *= l[j];
      z *= (p - l[j]);
    }

    r = r / (4 * sqrt(z));

    printf("%.3lf %.3lf %.3lf\n", xc, yc, r);


  }
  return 0;
}