Go: package main

import (
	"bufio"
	"fmt"
	"io"
	"math"
	"os"
	"strconv"
	"strings"

)


func main() {
	solve(os.Stdin, os.Stdout)
}

type ReaderEx struct {
	baseScanner *bufio.Scanner
	words       []string
	nextWordIdx func() int
	initWordIdx func(int)
}

func NewScannerEx(stdin io.Reader) *ReaderEx {
	var this ReaderEx
	var idx int
	var wordsCnt int
	this.baseScanner = bufio.NewScanner(stdin)
	this.baseScanner.Buffer(make([]byte, 0), 1E+11)
	this.nextWordIdx = func() int {
		cur := idx
		idx = (idx + 1) % wordsCnt
		return cur
	}
	this.initWordIdx = func(wc int) {
		idx = 0
		wordsCnt = wc
	}
	return &this
}

func (me *ReaderEx) Scan(doSplit bool) (isScanned bool) {
	isScanned = me.baseScanner.Scan()
	if doSplit {
		me.words = strings.Fields(me.baseScanner.Text())
	} else {
		me.words = []string{me.baseScanner.Text()}
	}
	me.initWordIdx(len(me.words))
	return
}

func (me *ReaderEx) nextBytes() []byte {
	return []byte(me.words[me.nextWordIdx()])
}
func (me *ReaderEx) nextString() string {
	return me.words[me.nextWordIdx()]
}

type StringArray []string

func (me *ReaderEx) nextStringArray() StringArray {
	return me.words[me.nextWordIdx():]
}

func (me StringArray) toStrings() []string {
	return me
}

func (me StringArray) toInts() []int {
	strValues := me.toStrings()
	values := make([]int, len(strValues))
	for i, v := range strValues {
		n, err := strconv.Atoi(v)
		if err != nil {
			panic(err)
		}
		values[i] = n
	}
	return values
}
func (me *ReaderEx) nextInt() int {
	n, err := strconv.Atoi(me.words[me.nextWordIdx()])

	defer func() {
		if err != nil {
			panic(fmt.Sprintf("getInt(%d)", n))
		}
	}()
	return n
}

func pow(x, y, mod int) (ans int) {

	ans = 1
	for bit := 1 << uint(math.Floor(math.Log2(float64(y)))); ; bit >>= 1 {
		if y&bit != 0 {
			ans *= x
			if mod > 0 {
				ans %= mod
			}
		}
		if bit <= 1 {
			return
		}
		ans *= ans
		if mod > 0 {
			ans %= mod
		}
	}
}

type factType struct {
	prime int
	count int
}

func fact(n int) (facts []*factType) {

	for i := 2; i*i <= n; i++ {
		if n%i == 0 {
			fa := factType{prime: i}
			for n%fa.prime == 0 {
				n /= fa.prime
				fa.count++
			}
			facts = append(facts, &fa)
		}
	}
	if n > 1 {
		facts = append(facts, &factType{prime: n, count: 1})
	}
	return facts
}
func dec2bin(n int) (ret []bool) {
	for bit := 1 << uint(math.Floor(math.Log2(float64(n)))); ; bit >>= 1 {
		ret = append(ret, n&bit != 0)

		if bit <= 1 {
			return
		}
	}

}

func abs(v int) int {
	if v < 0 {
		v = -v
	}
	return v
}

func b2i(b bool) (i int) {
	if b {
		i = 1
	} else {
		i = 0
	}
	return
}

func solve(stdin io.Reader, stdout io.Writer) {

	r := NewScannerEx(stdin)
	r.Scan(true)
	n := r.nextInt()

	type Vec struct {
		x, y float64
	}
	vec := func(a, b Vec) Vec { return Vec{b.x - a.x, b.y - a.y} }
	unv := func(a Vec) Vec { return Vec{-a.y, a.x} }
	cdot := func(a, b Vec) float64 { return a.x*b.x + a.y*b.y }
	times := func(t float64, a Vec) Vec { return Vec{t * a.x, t * a.y} }
	add := func(a, b Vec) Vec { return Vec{a.x + b.x, a.y + b.y} }
	for i := 0; i < n; i++ {

		r.Scan(true)
		nextFloat64 := func() (ret float64) { fmt.Sscanf(r.nextString(), "%f", &ret); return }
		a1, a2, a3 := Vec{nextFloat64(), nextFloat64()}, Vec{nextFloat64(), nextFloat64()}, Vec{nextFloat64(), nextFloat64()}
		unv23 := unv(vec(a2, a3))
		v12 := vec(a1, a2)
		v31 := vec(a3, a1)
		s := cdot(v12, v31) / 2 / cdot(v12, unv23)
		c := add(times(.5, add(a2, a3)), times(s, unv23))
		v1c := vec(a1, c)
		fmt.Fprintf(stdout, "%.3f %.3f %.3f\n", c.x, c.y, math.Sqrt(v1c.x*v1c.x+v1c.y*v1c.y))
	}
}

C++: #include <iostream>
#include <cmath>
#include <iomanip>
#define sqr(x) ((x) * (x))
using namespace std;

void equation(double a, double b, double c, double d, double e, double f, double *x, double *y)
{
  *x = (c * e - b * f) / (a * e - b * d);
  *y = (a * f - c * d) / (a * e - b * d);   
}


int main()
{
  int n;
  double x1, y1, x2, y2, x3, y3, x, y;
  cin >> n;
  for(int i = 0; i < n; i++){
    cin >> x1 >> y1 >> x2 >> y2 >> x3 >> y3;
    x = y = 0;
    equation((2 * (x2 - x1)), (2 * (y2 - y1)), (sqr(x2) + sqr(y2) - sqr(x1) - sqr(y1)), (2 * (x3 - x2)), (2 * (y3 - y2)), (sqr(x3) + sqr(y3) - sqr(x2) - sqr(y2)), &x, &y);
    double r = sqrt(sqr(x1 - x) + sqr(y1 - y));
    cout << fixed << setprecision(3) << x + 0.0001 << ' ' <<  y + 0.0001 << ' ' << r + 0.0001 << endl;
  }
}

C++: #include <cmath>
#include <cstdio>

using namespace std;

inline double sq(double x) {
  return x * x;
}

inline double det(double a, double b, double c, double d) {
  return a * d - b * c;
}

int main() {
  int N;
  scanf("%d", &N);
  for (int I = 0; I < N; I++) {
    double x[3], y[3];
    for (int i = 0; i < 3; i++)
      scanf("%lf%lf", x+i, y+i);
    double a = 2*(x[1]-x[0]),
           b = 2*(y[1]-y[0]),
           c = 2*(x[2]-x[0]),
           d = 2*(y[2]-y[0]),
           e = sq(x[1])-sq(x[0])+sq(y[1])-sq(y[0]),
           f = sq(x[2])-sq(x[0])+sq(y[2])-sq(y[0]),
           p = det(e, b, f, d) / det(a, b, c, d),
           q = det(a, e, c, f) / det(a, b, c, d),
           r = sqrt(sq(p-x[0])+sq(q-y[0]));
    p = round(p * 1000.0) / 1000.0;
    q = round(q * 1000.0) / 1000.0;
    r = round(r * 1000.0) / 1000.0;
    printf("%.3f %.3f %.3f\n", p, q, r);
  }
  return 0;
}

C++: #include<cstdio>
#include<cmath>

int main(){
	double x1,y1,x2,y2,x3,y3,p,q,r;
	int n;
	scanf("%d", &n);
	for(int i = 0; i < n; i++){
		scanf("%lf %lf %lf %lf %lf %lf",&x1,&y1,&x2,&y2,&x3,&y3);
		p = ((y1-y3)*(y1*y1 -y2*y2 +x1*x1 -x2*x2) -(y1-y2)*(y1*y1 -y3*y3 +x1*x1 -x3*x3)) / (2*(y1-y3)*(x1-x2)-2*(y1-y2)*(x1-x3));
		q = ((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));
		r = sqrt((x1 - p) * (x1 - p) + (y1 - q) * (y1 - q));
		printf("%.3f %.3f %.3f\n", p, q, r);
	}
	return 0;
}

C++: #include <iostream>
#include <vector>
#include <math.h>
#include <cstdio>
#include <algorithm>
using namespace std;

double renritux(double a,double b,double c,double d,double e,double f) 
{

	double x;	

		if (a==0){
			x = (f - (e*c/b)) / d;
		}else if(b==0){
			x = c / a;
		}else if(d==0){
			x = (c - (b*f/e)) / a;
		}else if(e==0){
			x = f / d;
		}else{
			x = (f - (e*c/b)) / (d - (e*a/b));
		}
		if (x==-0) x=0;
		
	return x;
  
}

double renrituy(double a,double b,double c,double d,double e,double f) 
{

	double y;	

		if (a==0){
			y = c / b;
		}else if(b==0){
			y = (f - (d*c/a)) / e;
		}else if(d==0){
			y = f / e;
		}else if(e==0){
			y = (c - (a*f/d)) / b;
		}else{
			y = (f - (d*c/a)) / (e - (d*b/a));
		}
		if (y==-0) y=0;
		
	return y;
  
}

double distance(double x1,double y1,double x2,double y2)
{
 
    vector<double> x,y;
    double dist;
    
    x.push_back(x1);
    y.push_back(y1);
    x.push_back(x2);
    y.push_back(y2);
     
    sort(x.begin(),x.end());
    sort(y.begin(),y.end());
     
    dist = sqrt((x[1]-x[0])*(x[1]-x[0])+(y[1]-y[0])*(y[1]-y[0]));
     
    return dist;
    
}

int main() {
	int n;
	cin >>n;
	
	for(int i=0;i<n;i++){
		double x1,y1,x2,y2,x3,y3,px,py,r,a,b,c,d,e,f;
		cin >>x1>>y1>>x2>>y2>>x3>>y3;
		
		if (y2!=y1){
			a = (x2-x1)/(y2-y1);
			b = 1;
			c = (x1+x2)*(x2-x1)/(2*(y2-y1)) + (y1+y2)/2;
		}else{
			a = 1;
			b = 0;
			c = (x1+x2)/2;
		}
		
		if (y3!=y1){
			d = (x3-x1)/(y3-y1);
			e = 1;
			f = (x1+x3)*(x3-x1)/(2*(y3-y1)) + (y1+y3)/2;
		}else{
			d = 1;
			e = 0;
			f = (x1+x3)/2;
		}
		px = renritux(a,b,c,d,e,f);
	  	py = renrituy(a,b,c,d,e,f);
	  	
	  	r = distance(px,py,x1,y1);
	  	
		printf("%.3f %.3f %.3f\n",px,py,r);
	
	}	
	return 0;
  
}