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 <cstdio>
#include <cassert>
#include <cmath>
#include <complex>
#include <vector>
#include <utility>
using namespace std;

typedef complex<double> Point;
#define X real()
#define Y imag()
#define EPS 10e-8

namespace std {
  bool operator < (Point a, Point b) {
    if (a.X != b.X) return a.X < b.X;
    return a.Y < b.Y;
  }
}

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

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

double dist2(Point a, Point b) {
  return dot(a-b, a-b);
}

struct Line : public vector<Point> {
  Line(Point a, Point b) {push_back(a); push_back(b);}
};

int n;
Point ps[3];

Line PerpendBisect(Line l) {
  Point mid = (l[0]+l[1])/2.0;
  return Line(mid, mid+(l[1]-l[0])*Point(0, 1));
}

Point GetCrossPoint(Line l, Line m) {
  double A = cross(l[1]-l[0], m[1]-m[0]);
  double B = cross(l[1]-l[0], l[1]-m[0]);
  if (abs(A) < EPS && abs(B) < EPS) return m[0];
  if (abs(A) < EPS) assert(false);
  return m[0] + B / A * (m[1]-m[0]);
}

double round3(double t) {
  return floor(t*1000+0.5)/1000.0;
}

int main() {
  scanf("%d", &n);
  while (n--) {
    for (int i=0; i<3; i++) {
      double x, y;
      scanf("%lf%lf", &x, &y);
      ps[i] = Point(x, y);
    }

    Line l(ps[0], ps[1]);
    Line m(ps[1], ps[2]);
    Point p = GetCrossPoint(PerpendBisect(l), PerpendBisect(m));
    double r = sqrt(dist2(p, ps[0]));
    printf("%.3f %.3f %.3f\n", round3(p.X), round3(p.Y), round3(r));
  }
}

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

using namespace std;

#define MAX 256

float LOSER(float x){
	if((int)(x*10000)%10 > 4)return x + 0.001;
	return x;
}

int main(void){
	int n,i = 0;
	float x1,y1,x2,y2,x3,y3;
	float px[MAX],py[MAX],r[MAX];
	
	cin >> n;
	while(i < n){
		cin >> x1 >> y1 >> x2 >> y2 >> x3 >> y3;
		px[i] = ((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));
		py[i] = ((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[i] = sqrt((px[i]-x1)*(px[i]-x1)+(py[i]-y1)*(py[i]-y1));
		px[i]=LOSER(px[i]);
		py[i]=LOSER(py[i]);
		r[i]=LOSER(r[i]);
		i++;
		printf("%.3f %.3f %.3f",px[i],py[i],r[i]);
	}

	return 0;
}

C++: #include<stdio.h>
#include<math.h>
double sisyagonyuu3(double moto){
	if(moto>0){
		return (moto+0.0005)/100*100;
	}else if(moto==0){
		return 0;
	}else{
		return (moto-0.0005)/100*100;
	}
}
int main()
{
	int n;
	double x1[32],x2[32],x3[32],y1[32],y2[32],y3[32],p,q,r,coa,sna;
	double ac,ab,bc;
	scanf("%d",&n);
	for(int i=0;i<n;i++){
		scanf("%lf%lf%lf%lf%lf%lf",&x1[i],&x2[i],&x3[i],&y1[i],&y2[i],&y3[i]);
		p=sisyagonyuu3(((y1[i]-y3[i])*(y1[i]*y1[i]-y2[i]*y2[i]+x1[i]*x1[i]-x2[i]*x2[i])-(y1[i]-y2[i])*(y1[i]*y1[i]-y3[i]*y3[i]+x1[i]*x1[i]-x3[i]*x3[i]))/(2*(y1[i]-y3[i])*(x1[i]-x2[i])-2*(y1[i]-y2[i])*(x1[i]-x3[i])));
		q=sisyagonyuu3(((x1[i]-x3[i])*(x1[i]*x1[i]-x2[i]*x2[i]+y1[i]*y1[i]-y2[i]*y2[i])-(x1[i]-x2[i])*(x1[i]*x1[i]-x3[i]*x3[i]+y1[i]*y1[i]-y3[i]*y3[i]))/(2*(x1[i]-x3[i])*(y1[i]-y2[i])-2*(x1[i]-x2[i])*(y1[i]-y3[i])));
		ab=sqrt(fabs((x3[i]-x1[i])*(x3[i]-x1[i])+(y3[i]-y1[i])*(y3[i]-y1[i])));
		ac=sqrt(fabs((x3[i]-x2[i])*(x3[i]-x2[i])+(y3[i]-y2[i])*(y3[i]-y2[i])));
		bc=sqrt(fabs((x2[i]-x1[i])*(x2[i]-x1[i])+(y2[i]-y1[i])*(y2[i]-y1[i])));
		coa=(ac*ac+ab*ab-bc*bc)/(2*ac*ab);
		sna=1-coa*coa;
		r=sisyagonyuu3(bc/(sna*2));
		printf("%.3lf %.3lf %.3lf\n",p,q,r);
	}
	return 0;
}
/*?????\???*/

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

#define SQ(x) (x * x)

int main(void)
{
  int N, i;
  double x1, x2, x3;
  double y1, y2, y3;
  double a, b, c, d, e, f;
  double l, m, n;
  double xp,yp, r;

  cin >> N;
  for (i = 0; i < N; i++){
    cin >> x1 >> y1 >> x2 >> y2 >> x3 >> y3;
    
    a = x1 - x2;
    b = y1 - y2;
    c = -1 * (SQ(x1) - SQ(x2) + SQ(y1) - SQ(y2));
    d = x1 - x3;
    e = y1 - y3;
    f = -1 * (SQ(x1) - SQ(x3) + SQ(y1) - SQ(y3));
    
    l = (c * e - b * f) / (e * a - b * d);
    m = (d * c - a * f) / (d * b - e * a);
    
    n = -1 * (SQ(x1) + SQ(y1) + l * x1 + m * y1);
    
    xp = l / -2.0;
    yp = m / -2.0;
    r = sqrt(SQ(l) + SQ(m) - 4 * n) / 2.0;
    
    printf("%.3f %.3f %.3f\n", xp, yp, r);
  }
  return 0;
}