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 <algorithm>
#include <cassert>
#include <cmath>
#include <stdio.h>

using namespace std;

//-------------------------------------------------------------------------
// geometric library

struct point {
	double x;
	double y;
};

struct circle {
	point center;
	double radius;
};

double get_distance(const point& p1, const point& p2)
{
	return sqrt(pow(p1.x - p2.x, 2) + pow(p1.y - p2.y, 2));
}

point get_midpoint(const point& p1, const point& p2)
{
	point mid;
	mid.x = p1.x + p2.x / 2.0;
	mid.y = p1.y + p2.y / 2.0;
	return mid;
}

std::istream& operator >> (std::istream& is, point& p)
{
	is >> p.x >> p.y;
	return is;
}

//-------------------------------------------------------------------------
// solution

// 外接円を求める
circle get_circum_circle(const point& p1, const point& p2, const point& p3)
{
	double a = get_distance(p1, p2);
	double b = get_distance(p2, p3);
	double c = get_distance(p3, p1);
	circle result;

	// 半径の公式
	result.radius = a * b * c / sqrt((a + b + c) * (-a + b + c) * (a - b + c) * (a + b - c));

	// c,p1,p2のなす角
	double theta = acos((a / 2.0) / result.radius);

	result.center.x = p1.x + result.radius * cos(theta);
	result.center.y = p1.y + result.radius * sin(theta);

	return result;
}

circle get_circum_circle(istream& is)
{
	point p1, p2, p3;
	is >> p1 >> p2 >> p3;
	return get_circum_circle(p1, p2, p3);
}

int main(void)
{
	int num_cases;

	std::cin >> num_cases;

	for (int i = 0; i < num_cases; i++) {		
		circle result = get_circum_circle(std::cin);
		printf("%.3f %.3f %.3f\n", result.center.x, result.center.y, result.radius);
	}
	return 0;
}

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

int main(void) {

  int data;
  double x1,y1,x2,y2,x3,y3;

  double x12,y12,x13,y13;
  double ang12,ang13;
  double xp,yp,r;

  int flag;
  int i;

  scanf("%d",&data);

  for(i=0;i<data;i++) {
    flag=1;
    scanf("%lf %lf %lf %lf %lf %lf",&x1,&y1,&x2,&y2,&x3,&y3);

    x12=(x1+x2)/2.0;
    y12=(y1+y2)/2.0;
    x13=(x1+x3)/2.0;
    y13=(y1+y3)/2.0;

    if(y1==y2) {

      xp=x12;

      ang13=-(x3-x1)/(y3-y1);

      yp=ang13*(xp-x13)+y13;

      flag=0;

    }

    if(y1==y3) {

      xp=x13;
      
      ang12=-(x2-x1)/(y2-y1);

      yp=ang12*(xp-x12)+y12;

      flag=0;

    }

    if(flag==1) {

      ang12=-(x2-x1)/(y2-y1);
      ang13=-(x3-x1)/(y3-y1);

      xp=(ang12*x12-ang13*x13-y12+y13)/(ang12-ang13);

      yp=ang12*(xp-x12)+y12;
    
    }

    r=sqrt((xp-x1)*(xp-x1)+(yp-y1)*(yp-y1));

    printf("%lf %lf %lf\n",xp,yp,r);
  }

  return 0;
  
}

C++: // AOJ 0010 (http://judge.u-aizu.ac.jp/onlinejudge/description.jsp?id=0010&lang=jp)
#include<cstdio>
#include<cmath>
#define rep(i,a) for(int i=0;i<(a);++i)

int n;

double sqr( double x )
{ return x*x; }

int main()
{
	scanf( "%d", &n );
	while( n-- )
	{
		double x1, y1, x2, y2, x3, y3;
		scanf( "%lf%lf%lf%lf%lf%lf", &x1, &y1, &x2, &y2, &x3, &y3 );

		double a = sqrt(sqr(x3-x2)+sqr(y3-y2)), b = sqrt(sqr(x1-x3)+sqr(y1-y3)), c = sqrt(sqr(x2-x1)+sqr(y2-y1));
		double cosA = (sqr(b)+sqr(c)-sqr(a))/(sqr(b)+sqr(c)), cosB = (sqr(c)+sqr(a)-sqr(b))/(sqr(c)+sqr(a)), cosC = (sqr(a)+sqr(b)-sqr(c))/(sqr(a)+sqr(b));
		double sinA = sqrt(1-sqr(cosA)), sinB = sqrt(1-sqr(cosB)), sinC = sqrt(1-sqr(cosC));
		double sin2A = 2*sinA*cosA, sin2B = 2*sinB*cosB, sin2C = 2*sinC*cosC;
		double px = (sin2A*x1+sin2B*x2+sin2C*x3)/(sin2A+sin2B+sin2C), py = (sin2A*y1+sin2B*y2+sin2C*y3)/(sin2A+sin2B+sin2C);

		printf( "%.3f %.3f %.3f\n", px, py, sqrt(sqr(x1-px)+sqr(y1-py)) );
	}

	return 0;
}

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

using namespace std;
struct point{
	double x, y;
};
struct circle{
	point p;
	double r;
};

circle circumscribed_circle(point p, point q, point r){
	double a[2],b[2],c[2];
	circle res;
     
    a[0]=2*(q.x-p.x);
    b[0]=2*(q.y-p.y);
    c[0]=p.x*p.x-q.x*q.x+p.y*p.y-q.y*q.y;
     
    a[1]=2*(r.x-p.x);
    b[1]=2*(r.y-p.y);
    c[1]=p.x*p.x-r.x*r.x+p.y*p.y-r.y*r.y;
     
    res.p.x=(b[0]*c[1]-b[1]*c[0])/(a[0]*b[1]-a[1]*b[0]);
    res.p.y=(c[0]*a[1]-c[1]*a[0])/(a[0]*b[1]-a[1]*b[0]);
  
    res.r=sqrt(pow(fabs(p.x-res.p.x),2)+pow(fabs(p.y-res.p.y),2));
     
    return res;
}

int main(){
	int n;
	point in[3];
	circle ans;
	cin>>n;
	for(;n--;){
		for(int i=0;i<3;i++)
			cin >> in[i].x >> in[i].y;
		ans = circumscribed_circle(in[0], in[1], in[2]);
		printf("%.3f %.3f %.3f\n",ans.p.x,ans.p.y,ans.r);
	}
	return 0;
}