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 <vector>
#include <math.h>

#define POW(X) (X)*(X)

using namespace std;

int main(){
  double x1,y1,x2,y2,x3,y3;
  vector<double> x1l,y1l,x2l,y2l,x3l,y3l;
  int n;

  cin >> n;

  for(int i=0; i<n; i++){
    cin >> x1 >> y1 >> x2 >> y2 >> x3 >> y3;
    x1l.push_back(x1);
    y1l.push_back(y1);
    x2l.push_back(x2);
    y2l.push_back(y2);
    x3l.push_back(x3);
    y3l.push_back(y3);
  }

  double ex,ey,fx,fy;
  double a,b,c,d,e,f,r;

  for(int i=0; i<n; i++){
    x1=x1l[i];
    y1=y1l[i];
    x2=x2l[i];
    y2=y2l[i];
    x3=x3l[i];
    y3=y3l[i];

    a = -((y2-y1)*POW(y3)+(-POW(y2)+POW(y1)-POW(x2)+POW(x1))*y3+y1*POW(y2)+(-POW(y1)+POW(x3)-POW(x1))*y2+(POW(x2)-POW(x3))*y1)/((2*x2-2*x1)*y3+(2*x1-2*x3)*y2+(2*x3-2*x2)*y1);
    b =  ((x2-x1)*POW(y3)+(x1-x3)*POW(y2)+(x3-x2)*POW(y1)+(x2-x1)*POW(x3)+(POW(x1)-POW(x2))*x3+x1*POW(x2)-POW(x1)*x2)/((2*x2-2*x1)*y3+(2*x1-2*x3)*y2+(2*x3-2*x2)*y1);
    r = sqrt((a-x1)*(a-x1) + (b-y1)*(b-y1));
    printf("%0.3f %0.3f %0.3f\n",a,b,r);
  }

  return 0;
}

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

double sisya(double x)
{
	int a = static_cast<int>(x * 10000);
	//x = static_cast<double>(static_cast<int>(x * 1000)) / 1000;
	if(a < 0 && a%10 <= -5)
		return x-0.001;
	else if(a%10 >= 5)
		return x+0.001;
	return x;
}

double dif(double x,double y,double xx, double yy)
{
	return sqrt((x-xx)*(x-xx)+(y-yy)*(y-yy));
}

int main()
{
	int n;
	double x1,x2,x3,y1,y2,y3;
	cin >> n;
	for(int i=0;i<n;i++){
		cin >> x1 >> y1 >> x2 >> y2 >> x3 >> y3;
		double px = sisya(max(x1,max(x2,x3)) - (max(x1,max(x2,x3)) - min(x1,min(x2,x3))) / 2 );
		double py = sisya(max(y1,max(y2,y3)) - (max(y1,max(y2,y3)) - min(y1,min(y2,y3))) / 2 );
		double r  = sisya(dif(x1,y1,px,py));
		cout << setprecision(3) << fixed << px << " " << setprecision(3) << fixed << py << " " << setprecision(3) << fixed << r <<endl;
	}
	return 0;
}

C++: #include <iostream>
#include <iomanip>
#include <cmath>

using namespace std;

void gaisetu(double x1,double y1,double x2,double y2,double x3,double y3){
  //center point.and r.
  double a,b,r;
  a = ((y2-y3)*(x1*x1-x2*x2+y1*y1-y2*y2) - (y1-y2)*(x2*x2-x3*x3+y2*y2-y3*y3))
    / (2*((x1-x2)*(y2-y3)-(x2-x3)*(y1-y2)));

  b = ((x2-x3)*(x1*x1-x2*x2+y1*y1-y2*y2) - (x1-x2)*(x2*x2-x3*x3+y2*y2-y3*y3))
    / (2*((y1-y2)*(x2-x3)-(y2-y3)*(x1-x2)));

  r = sqrt((a-x1)*(a-x1) + (b-y1)*(b-y1));

  cout << fixed << setprecision(3) << a << " " <<  b << " " << r <<  endl;
}
int main(){
  //gaisetu(0.0,0.0,2.0,0.0,2.0,2.0);
  int n;
  cin >> n;
  for(int i=0;i<n;i++){
    double x1,y1,x2,y2,x3,y3;
    cin >> x1 >> y1 >> x2 >> y2 >> x3 >> y3;
    gaisetu(x1,y1,x2,y2,x3,y3);
  }
  return 0;
}

C++: #include <iostream>
#include <cstdio>
#include <cstring>
#include <algorithm>
#include <complex>
using namespace std;

#define x real()
#define y imag()
typedef complex<double> Point;

Point circumscribed_Circle_Center(Point a, Point b, Point c){
  double A = a.x - b.x;
  double B = a.y - b.y;
  double C = -1 * (a.x*a.x - c.x*c.x + a.y*a.y - b.y*b.y);
  double D = a.x - c.x;
  double E = a.y - c.y;
  double F = -1 * (a.x*a.x - c.x*c.x + a.y*a.y - c.y*c.y);

  double L = (C*E - B*F) / (E*A - B*D);
  double M = (D*C - A*F) / (D*B - E*A);
  double xp = L / -2.0;
  double yp = M / -2.0;
  return (Point(xp, yp));
}

double circumscribed_Circle_Radius(Point a, Point c){
  double L = c.x * -2.0;
  double M = c.y * -2.0;
  double N = -1 * (a.x*a.x + a.y*a.y + L*a.x + M*a.y);
  double r = sqrt(L*L + M*M - 4*N) / 2.0;
  return r;
}

int main(){
  int n;
  Point a, b, c;
  cin >> n;
  while(n--){
    cin >> a.x >> a.y >> b.x >> b.y >> c.x >> c.y;
    Point C = circumscribed_Circle_Center(a, b, c);
    double r = circumscribed_Circle_Radius(a, C);
    printf("%.3f %.3f %.3f\n", C.x, C.y, r);
  }
  return 0;
}