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 <bits/stdc++.h>
#include<stdio.h>
using namespace std;
#define FOR(i,k,n) for(int i = (k); i < (n); i++)
#define REP(i,n) FOR(i,0,n)
#define ALL(a) begin(a),end(a)
#define MS(m,v) memset(m,v,sizeof(m))
#define D10  fixed<<setprecision(3)
typedef vector<int> vi;
typedef vector<string> vs;
typedef pair<int, int> P;
typedef long long ll;
const ll INF = 114514810;
const ll MOD = 1000000007;
const double EPS = 1e-8;
struct edge
{
	int from, to, cost;
	bool operator < (const edge& e) const { return cost < e.cost; }
	bool operator >(const edge& e) const { return cost > e.cost; }
};
int dx[] = { -1, 0, 0, 1 }; int dy[] = { 0, -1, 1, 0 };
template<class T> T &chmin(T &a, const T &b) { return a = min(a, b); }
template<class T> T &chmax(T &a, const T &b) { return a = max(a, b); }
bool valid(int x, int y, int h, int w) { return (x >= 0 && y >= 0 && x < h&&y < w); }
///*************************************************************************************///
///*************************************************************************************///
///*************************************************************************************///

const double PI = acos(-1.0);
bool eq(double a, double b) { return fabs(a - b) < EPS; }
typedef complex<double> Point;
typedef vector<Point> Polygon;

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

struct Line
{
	Point a, b;
	Line(Point p, Point q) :a(p), b(q) {};
};

struct Circle
{
	Point p; double r;
	Circle(Point a, double b) :p(a), r(b) {};
};

double dot(Point a, Point b)
{
	return real(conj(a)*b);
}

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

int ccw(Point a, Point b, Point c)
{
	b -= a; c -= a;
	if (cross(b, c) > EPS) return 1;	//counter cloclwise
	if (cross(b, c) < -EPS) return -1;  //cloclwise
	if (dot(b, c) < 0) return 2;		//c--a--b on line 
	if (norm(b) < norm(c)) return -2;   //a--b--c on line
	return 0;							//a--c--b on line
}

bool isis_ll(Line l, Line m)
{
	return abs(cross(l.b - l.a, m.b - m.a)) > EPS;
}

bool isis_ls(Line l, Line s)
{
	return cross(l.b - l.a, s.a - l.a)*cross(l.b - l.a, s.b - s.a) < EPS;
}

bool isis_ss(Line s, Line t)
{
	return (ccw(s.a, s.b, t.a)*ccw(s.a, s.b, t.b) <= 0 &&
		ccw(t.a, t.b, s.a)*ccw(t.a, t.b, s.b) <= 0);
}

bool isis_lp(Line l, Point p)
{
	return (abs(cross(l.b - p, l.a - p)) < EPS);
}

bool isis_sp(Line s, Point p)
{
	return (abs(s.a - p) + abs(s.b - p) - abs(s.b - s.a)) < EPS;
}

Point projection(Line l, Point p)
{
	Point base = l.b - l.a;
	double r = dot(p - l.a, base) / norm(base);
	return l.a + base*r;
}

Point mirror(Line l, Point p)
{
	return 2.0*projection(l, p) - p;
}

double dist_lp(Line l, Point p)
{
	return abs(p - projection(l, p));
}

double dist_ll(Line l, Line m)
{
	return isis_ll(l, m) ? 0 : dist_lp(l, m.a);
}

double dist_ls(Line l, Line s)
{
	if (isis_ls(l, s)) return 0;
	return min(dist_lp(l, s.a), dist_lp(l, s.b));
}

double dist_sp(Line s, Point p)
{
	Point r = projection(s, p);
	if (isis_sp(s, r)) return abs(r - p);
	return min(abs(s.a - p), abs(s.b - p));
}

double dist_ss(Line s, Line t)
{
	if (isis_ss(s, t)) return 0;
	return min(min(dist_sp(s, t.a), dist_sp(s, t.b)), min(dist_sp(t, s.a), dist_sp(t, s.b)));
}

Point is_ll(Line s, Line t)
{
	double a = cross(s.b - s.a, t.b - t.a);
	double b = cross(s.b - s.a, s.b - t.a);
	return t.a + b / a*(t.b - t.a);
}

int main()
{
	int n;
	while (cin >> n)
	{
		double x[3], y[3];
		REP(i, 3) cin >> x[i] >> y[i];
		Point p(x[0], y[0]), q(x[1], y[1]), r(x[2], y[2]);
		Point s = q - p, t = r - p;
		s *= exp(Point(0, PI / 2));
		t *= exp(Point(0, PI / 2));
		Line a((p + q)*0.5, (p + q)*0.5 + s);
		Line b((p + r)*0.5, (p + r)*0.5 + t);
		Point ans = is_ll(a, b);
		cout << D10 << ans.real() << " " << ans.imag() << " " << abs(ans - p) << endl;
	}
	return 0;
}

C++: #include <iostream>
#include <cmath>
using namespace std;
int main() {
    cin.tie(0);
    ios::sync_with_stdio(false);
    int n; cin >> n;
    double x1, y1, x2, y2, x3, y3;
    while (n--) {
        cin >> x1 >> y1 >> x2 >> y2 >> x3 >> y3;

        if (y1 == y3) {
            swap(x3, x2);
            swap(y3, y2);
        }
        if (y2 == y3) {
            swap(x3, x1);
            swap(y3, y1);
        }
        double px, py, r;
        double a = x2 - x3;
        double b = y2 - y3;
        double c = x2 + x3;
        double d = y2 + y3;
        double e = x3 - x1;
        double f = y3 - y1;
        double g = x3 + x1;
        double h = y3 + y1;
        px = ((a/b)*(c/2) + d/2 - (e/f)*(g/2) - h/2) / (a/b - e/f);
        py = -(a/b) * px + (a/b) * c/2 + d/2;
        r = sqrt((x1 - px) * (x1 - px) + (y1 - py) * (y1 - py));

        cout.precision(3);
        cout << fixed << px << " " << py << " " << r << "\n";
    }
    return 0;
}

C++: /* Karen {{{
  ___  ____
 |_  ||_  _|
   | |_/ /    ,--.   _ .--.  .---.  _ .--.
   |  __'.   `'_\ : [ `/'`\]/ /__\\[ `.-. |
  _| |  \ \_ // | |, | |    | \__., | | | |
 |____||____|\'-;__/[___]    '.__.'[___||__]
}}} */
// include {{{
#include <map>
#include <set>
#include <stack>
#include <queue>
#include <cmath>
#include <math.h>
#include <string>
#include <vector>
#include <complex>
#include <iostream>
#include <algorithm>

using namespace std;

// }}}
/* cpp template {{{*/


#define endl '\n'
#define REP(i, n) for (int i = 0; i < (n); i++)
#define REPS(i, a, n) for (int i = (a); i < (n); i++)
#define RREP(i, n) for (int i = 1; i <= (n); i++)
#define X real()
#define Y imag()
#define EQ(n,m) (abs((n)-(m)) < EPS)

typedef double D;      // ??§?¨?????????????double???long double?????????
typedef long long ll;
typedef long double lb;
typedef complex<D> P;  // Point
typedef pair<P, P> L;  // Line
typedef vector<P> VP;
typedef vector<int> vi;
typedef vector<vector<int> > vii;
typedef pair<int, int> pii;
typedef pair<int, string> pis;
typedef pair<string, int> psi;

inline bool inside(int y, int x, int H, int W){return (y >= 0 && x >= 0 && y < H && x < W);}
inline int in() {int x; std::cin >> x; return x;}

template <typename T>
void print(std::vector<T>& v, char c = ' ') {
  REP(i, v.size()) {
    if (i != 0) std::cout << c;
    std::cout << v[i];
  }
  std::cout << endl;
}
template <typename T>
void print(T x) {
  std::cout << x << '\n';
}

/* ?????° */
const ll MOD = 1e9 + 7;
const ll INF = 1e9 + 9;
const D EPS  = 1e-9;
const int dx[] = {0, 1, 0, -1, 1, -1, 1, -1};
const int dy[] = {1, 0, -1, 0, 1, -1, -1, 1};


/* }}} */

D cross(P a, P b) {
  return (conj(a)*b).Y;
}

P crosspointLL(P a1, P a2, P b1, P b2) {
  D d1 = cross(b2-b1, b1-a1);
  D d2 = cross(b2-b1, a2-a1);
  if (EQ(d1, 0) && EQ(d2, 0)) return a1;  // same line
  if (EQ(d2, 0)) throw "kouten ga nai";   // ???????????????
  return a1 + d1/d2 * (a2-a1);
}

P circumcenter(P a, P b, P c) {
  a = (a-c)*0.5;
  b = (b-c)*0.5;
  return c + crosspointLL(a, a*P(1,1), b, b*P(1,1));
}

int main()
{
  cin.tie(0);
  ios::sync_with_stdio(false);

  int x = in();
  
  for (int i = 0; i < x; i++){
    D a1, a2, b1, b2, c1, c2;
    cin >> a1 >> a2 >> b1 >> b2 >> c1 >> c2;
    P p = circumcenter( P(a1, a2), P(b1, b2), P(c1, c2));
    D r = sqrt(pow(a1 - p.X, 2) + pow(a2 - p.Y, 2));
    printf("%.3f %.3f %.3f", p.X, p.Y, r);

    cout << endl;
  }
  return (0);
}