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<cmath>
int main()
{
	int n;
	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 x4 = (x1 + x2) / 2, y4 = (y1 + y2) / 2, x5 = (x1 + x3) / 2, y5 = (y1 + y3) / 2;
		double a1, a2, b1, b2, c1, c2;
		if(x1 == x2)
		{
			a1 = 0.0;
			b1 = 1.0;
			c1 = y4;
		}
		else if(y1 == y2)
		{
			b1 = 0.0;
			a1 = 1.0;
			c1 = x4;
		}
		else
		{
			b1 = 1.0;
			a1 = - 1 / ((y2 - y1) / (x2 - x1));
			c1 = a1 * x4 + b1 * y4;
		}
		if(x1 == x3)
		{
			a2 = 0.0;
			b2 = 1.0;
			c2 = y5;
		}
		else if(y1 == y3)
		{
			b2 = 0.0;
			a2 = 1.0;
			c2 = x5;
		}
		else
		{
			b2 = 1.0;
			a2 = - 1 / ((y3 - y1) / (x3 - x1));
			c2 = a2 * x5 + b2 * y5;
		}
		double x11 = a1, x12 = b1, x13 = c1, x14 = a2, x15 = b2, x16 = c2;
		x11 *= b2;
		x13 *= b2;
		x14 *= b1;
		x16 *= b1;
		double t1 = (x13 - x16) / (x11 - x14);
		b1 *= a2;
		c1 *= a2;
		b2 *= a1;
		c2 *= a1;
		double t2 = (c1 - c2) / (b1 - b2);
		if(t1 == -0.0) t1 = 0.0;
		if(t2 == -0.0) t2 = 0.0;
		double t3 = sqrt((x1 - t1) * (x1 - t1) + (y1 - t2) * (y1 - t2));
		printf("%.3lf %.3lf %.3lf\n", t1, t2, t3);
	}
	return 0;
}

C++: #include <iostream>
#include <stdio.h>
#include <vector>
#include <string>
#include <sstream>
#include <algorithm>
#include <complex>
#include <map>
using namespace std;
typedef long long ll;
typedef pair<int, int> PII;
typedef vector<int> VI;
typedef vector<VI> VVI;
#define rep(i,n) for (int i=0; i < (n); i++)

typedef double D;      // 座標値の型。doubleかlong doubleを想定
typedef complex<D> P;  // Point
typedef pair<P, P> L;  // Line
typedef vector<P> VP;
const D EPS = 1e-9;    // 許容誤差。問題によって変える
#define X real()
#define Y imag()
#define LE(n,m) ((n) < (m) + EPS)
#define GE(n,m) ((n) + EPS > (m))
#define EQ(n,m) (abs((n)-(m)) < EPS)

// 内積　dot(a,b) = |a||b|cosθ
D dot(P a, P b) {
  return (conj(a)*b).X;
}
// 外積　cross(a,b) = |a||b|sinθ
D cross(P a, P b) {
  return (conj(a)*b).Y;
}

// 2直線の交点
P crosspointLL(P a1, P a2, P b1, P b2) {
  D d1 = cross(b2-b1, b1-a1);
  D d2 = cross(b2-b1, a2-a1);
  if (EQ(d1, 0) && EQ(d2, 0)) return a1;  // same line
  if (EQ(d2, 0)) throw "kouten ga nai";   // 交点がない
  return a1 + d1/d2 * (a2-a1);
}

// 三角形の外心。点a,b,cは同一線上にあってはならない
P circumcenter(P a, P b, P c) {
  a = (a-c)*0.5;
  b = (b-c)*0.5;
  return c + crosspointLL(a, a*P(1,1), b, b*P(1,1));
}

int main() {
  int n;
  cin >> n;
  D x1,y1,x2,y2,x3,y3;
  rep(_,n) {
    cin >> x1 >> y1 >> x2 >> y2 >> x3 >> y3;
    P a = P(x1,y1);
    P b = P(x2,y2);
    P c = P(x3,y3);
    P center = circumcenter(a,b,c);
    printf("%.6lf %.6lf %.6lf\n", center.X, center.Y, abs(center - a));
  }
  return 0;
}

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

class Point {
public:
  double x, y;
  Point(double x=0, double y=0) : x(x), y(y) {}
};

double dist(Point p1, Point p2) {
  return sqrt(pow(p1.x-p2.x, 2.0)+pow(p1.y-p2.y, 2.0));
}

double LawOfCosines(double a, double b, double c) {
  return acos( (b*b+c*c-a*a) / (2.0*b*c) );
}

Point circumcenter(Point pa, Point pb, Point pc) {
  /*
  double A = abs(atan2(pb.y-pa.y, pb.x-pa.x) - atan2(pc.y-pa.y, pc.x-pa.x));
  double B = abs(atan2(pa.y-pb.y, pa.x-pb.x) - atan2(pc.y-pb.y, pc.x-pb.x));
  double C = abs(atan2(pa.y-pc.y, pa.x-pc.x) - atan2(pb.y-pc.y, pb.x-pc.x));
  */
  double a = dist(pb, pc);
  double b = dist(pa, pc);
  double c = dist(pa, pb);
  double A = LawOfCosines(a, b, c);
  double B = LawOfCosines(b, c, a);
  double C = LawOfCosines(c, a, b);
  return Point((pa.x*sin(A*2)+pb.x*sin(B*2)+pc.x*sin(C*2))
	       /(sin(A*2)+sin(B*2)+sin(C*2)),
	       (pa.y*sin(A*2)+pb.y*sin(B*2)+pc.y*sin(C*2))
	       /(sin(A*2)+sin(B*2)+sin(C*2))
	       );
}

main() {
  Point p[3];
  Point op;
  int n;
  cin >> n;
  for(int i = 0; i < n; i++) {
    for(int j = 0; j < 3; j++) cin >> p[j].x >> p[j].y;
    op = circumcenter(p[0], p[1], p[2]);
    /*double A = abs(atan2(p[1].y-p[0].y, p[1].x-p[0].x)
		   - atan2(p[2].y-p[0].y, p[2].x-p[0].x));*/
    printf("%.3f %.3f %.3f\n", op.x, op.y, dist(op,p[0]));
  }
}