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 <vector>
#include <string>
#include <stack>
#include <queue>
#include <deque>
#include <set>
#include <map>
#include <algorithm>	// require sort next_permutation count __gcd reverse etc.
#include <cstdlib>	// require abs exit atof atoi 
#include <cstdio>		// require scanf printf
#include <functional>
#include <numeric>	// require accumulate
#include <cmath>		// require fabs
#include <climits>
#include <limits>
#include <cfloat>
#include <iomanip>	// require setw
#include <sstream>	// require stringstream 
#include <cstring>	// require memset
#include <cctype>		// require tolower, toupper
#include <fstream>	// require freopen
#include <ctime>		// require srand
#define rep(i,n) for(int i=0;i<(n);i++)
#define ALL(A) A.begin(), A.end()

using namespace std;

typedef long long ll;
typedef pair<double, double> P;
typedef pair<double,P> dP;

dP calc_eq (double xa, double ya, double xb, double yb )
{
	double a = (xb - xa );
	double b = (yb - ya );
	double c = (xb - xa)*(xb + xa )/2. + (yb - ya)*(yb+ya )/2.;

	return dP (a, P (b, c ) );		
}

double calc_radius (int xa, int ya, int xb, int yb )
{
	double res = (xa - xb)*(xa - xb) + (ya - yb)*(ya - yb );

	return sqrt (res );
}

int main()
{
//	cut here before submit 
//	freopen ("testcase.CCT", "r", stdin );
	int n;
	cin >> n;
	rep (i, n ){
		double x1, y1, x2, y2, x3, y3;
		cin >> x1 >> y1 >> x2 >> y2 >> x3 >> y3;
		dP l1 = calc_eq (x1, y1, x2, y2 );
		dP l2 = calc_eq (x1, y1, x3, y3 );

		double a = l1.first, b = l1.second.first, c = l1.second.second;
		double d = l2.first, e = l2.second.first, f = l2.second.second;
/*
		cerr << "a: " << a << " b: " << b << " c: " << c << endl;
		cerr << "d: " << d << " e: " << e << " f: " << f << endl;
*/
		double x = 0.0, y = 0.0, r = 0.0;
		x = (c*e - b*f)/(a*e - b*d);
		y = (c*d - a*f)/(b*d - a*e);
		r = calc_radius (x, y, x1, y1 );

		if (fabs(x) < 1.0e-3){
			x = 0.0;
		} // end if
		if (fabs(y) < 1.0e-3){
			y = 0.0;
		} // end if

		printf ("%.3f %.3f %.3f\n", x, y, r );

	} // end loop

//	printf ("%d\n", res );
		
	return 0;
}

C++: #include <iostream>
#include <fstream>
#include <algorithm>
#include <vector>
#include <string>
#include <functional>
#include <array>
#include <stack>
#include <queue>
#include <chrono>
#include <numeric>
#include <memory.h>
#include <map>
#include <math.h>
#include <utility>


#pragma warning(disable:4996)
using namespace std;
#define REP(i,n) for(int i = 0 ; i < n ; ++i)
typedef long long Int;
const double PI = 3.141592653589793238;
const Int INF = 999999999999;
typedef pair<int, int> P;


double A[2][2];
double C[2];


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

		double x21 = x2 - x1;
		double x31 = x3 - x1;
		double y21 = y2 - y1;
		double y31 = y3 - y1;

		double xc = ((y31*(x21*x21 + y21*y21)) - (y21*(x31*x31 + y31*y31))) /
			(2 * (x21*y31 - y21*x31));

		double yc = ((x21*(x31*x31 + y31*y31)) - (x31*(x21*x21 + y21*y21))) /
			(2 * (x21*y31 - y21*x31));	
		
		double d = (xc - x1)*(xc - x1) + (yc - y1)*(yc - y1);
		int xc_ = xc * 1000;
		int yc_ = yc * 1000;
		xc_ += (xc_ % 10) > 4 ? 1 : 0;
		yc_ += (yc_ % 10) > 4 ? 1 : 0;

		printf("%.3lf %.3lf %.3lf", xc, yc, sqrt(d));


	}

}

C++: int main(){
	double x1 , y1 , x2 , y2 , x3 , y3;
	double a1 , b1 , c1 , a2 , b2 , c2;
	double a , b , c;
	double px , py , r;
	double tmp;
	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;
	px=(b1*c2-b2*c1)/(a1*b2-a2*b1);
	py=(c1*a2-c2*a1)/(a1*b2-a2*b1);
	a=sqrt((x1-x2)*(x1-x2)+(y1-y2)*(y1-y2));
	b=sqrt((x2-x3)*(x2-x3)+(y2-y3)*(y2-y3));
	c=sqrt((x3-x1)*(x3-x1)+(y3-y1)*(y3-y1));
	//(a/(2*r))*(a/(2*r))+((b*b-c*c-2a)/2*b*c)*((b*b-c*c-2a)/2*b*c)=1
	r=a/(2*sqrt(1-((b*b+c*c-a*a)/(2*b*c))*((b*b+c*c-a*a)/(2*b*c))));
	tmp=px*1000+0.5;
	px=(int)tmp;
	px/=1000;
	tmp=px*1000+0.5;
	py=(int)tmp;
	py/=1000;
	tmp=r*1000+0.5;
	r=(int)tmp;
	r/=1000;
	cout << fixed << setprecision(3) << px << " " << py << " " << r << endl;
	return 0;
}

C++: #include<iostream>
#include<cstdio>
#define _USE_MATH_DEFINES
#include<cmath>
#include<vector>
#include<map>
using namespace std;


#define INF 1e+10
#define EPS 1e-10
#define EQ(a,b) (abs(a-b)<EPS)

//誤差を考慮して足し算
double add(double a,double b){
	if(abs(a+b) < EPS*(abs(a)+abs(b)))return 0;
	return a+b;
}
struct P{//2次元ベクトル
	double x,y;
	P(){}
	P(double x,double y):x(x),y(y){}
	P operator + (P p){
		return P(add(x,p.x),add(y,p.y));
	}
	P operator - (P p){
		return P(add(x,-p.x),add(y,-p.y));
	}
	P operator * (double d){
		return P(x*d,y*d);
	}
	P operator / (double d){
		return P(x/d,y/d);
	}
	double dot(P p){//内積
		return add(x*p.x,y*p.y);
	}
	double det(P p){//外積
		return add(x*p.y,-y*p.x);
	}
	bool equal(P p){
		return (x-p.x)*(x-p.x)+(y-p.y)*(y-p.y) < EPS*EPS;
	}
};
//typedef pair<P,P> Line;

//線分p1-p2上に点qがあるか判定
bool on_seg(P p1,P p2,P q){
	return (p1-q).det(p2-q)==0 && (p1-q).dot(p2-q)<=0;
}
//直線p1-p2と直線q1-q2の交点
P intersection(P p1,P p2,P q1,P q2){
	return p1+(p2-p1)*( (q2-q1).det(q1-p1)/(q2-q1).det(p2-p1) );
}


//線分p1-p2と線分q1-q2が交差するか
bool intersecting(P p1,P p2,P q1,P q2){
	if(on_seg(p1,p2,q1)||on_seg(p1,p2,q2)||on_seg(q1,q2,p1)||on_seg(q1,q2,p2))return true;
	if((p1-p2).det(q1-q2)==0 )return false;//平行
	P a=intersection(p1,p2,q1,q2);
	return on_seg(p1,p2,a) && on_seg(q1,q2,a);
}
//原点中心回転
P rotate(P p,double rad){
	double s=sin(rad),c=cos(rad);
	return P(c*p.x-s*p.y, s*p.x+c*p.y);
}
//originを中心回転
P rotate(P p,double rad,P origin){
	return origin + rotate(p - origin,rad);
}
//二点間の距離
double dist(P p,P q){
	p = p-q;
	return sqrt(p.x*p.x+p.y*p.y);
}
//単位ベクトルに変換
P to_unit(P p){
	double d = sqrt(p.x*p.x+p.y*p.y);
	return p/d;
}
//円同士の交点を計算
pair<P,P> circle_intersection(double x1,double y1,double r1,double x2,double y2,double r2){
	double rad = atan2(y2-y1,x2-x1);
	x2 -= x1;
	y2 -= y1;
	P tmp = rotate(P(x2,y2),-rad);
	x2 = tmp.x;
	y2 = tmp.y;
	double x = (r1*r1-r2*r2+x2*x2)/(2*x2);
	if(abs(r1) < abs(x))return make_pair(P(0,0),P(0,0));//交点なし
	double y = sqrt(r1*r1-x*x);
	return make_pair( P(x1,y1)+rotate(P(x,y),rad) ,  P(x1,y1)+rotate(P(x,-y),rad) );
}
//線分と点の距離
double dist_lp(P p1,P p2,P q){
	double dx,dy;
	dx = p1.x-p2.x;
	dy = p1.y-p2.y;
	double d = min(dist(p1,q) ,dist(p2,q));
	pair<P,P> normal= make_pair(q+to_unit(P(-dy,dx))*d ,q+to_unit(P(dy,-dx))*d);//法線ベクトル
	if(intersecting(p1,p2,normal.first,normal.second)){
		return dist(q, intersection(p1,p2,normal.first,normal.second));
	}
	return d;
}
//線分同士の距離
double dist_ll(P p1,P p2,P q1,P q2){
	if(intersecting(p1,p2,q1,q2))return 0;
	return min( min(dist_lp(p1,p2,q1),dist_lp(p1,p2,q2))
		,min(dist_lp(q1,q2,p1),dist_lp(q1,q2,p2)) );
}
//ラジアンに変換
double radian(double angle){
	return angle/180.0*M_PI;
}


int main(){
	P a,b,c,g;
	int n;
	cin>>n;
	for(int i=0;i<n;i++){
		cin>>a.x>>a.y;
		cin>>b.x>>b.y;
		cin>>c.x>>c.y;
		g = intersection((a+b)/2,(a+b)/2+P(-(a.x-b.y),a.x-b.x),
			    (a+c)/2,(a+c)/2+P(-(a.x-c.y),a.x-c.x) );
		printf("%.3f %.3f %.3f\n",g.x,g.y,dist(g,a));
	}
	return 0;
}