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 <math.h>
 #include <string>
using namespace std;

int main() {
	int n;
	cin>>n;
	for(int h=0;h<n;h++){
double x1,y1,x2,y2,x3,y3,x2m,x3m,y2m,y3m,x21,y21,x31,y31,xy21,xans,yans;
cin>>x1>>y1>>x2>>y2>>x3>>y3;
	x2m=(x1+x2)/2;
	y2m=(y1+y2)/2;
	x3m=(x1+x3)/2;
	y3m=(y1+y3)/2;
	x21=x2-x1;
	x31=x3-x1;
	y21=y2-y1;
	y31=y3-y1;
	
	
if(y1!=y2){
	xy21=x21/y21;
	xans=(x31*x3m+y31*xy21*x2m+y3m-y2m)/(x31+y31*xy21);
	yans=xy21*(xans-x2m)+y2m;
}	
else{
	xans=x2m;
	yans=(x3m-xans)*x31/y31+y3m;
}
double r;
r=sqrt((xans-x1)*(xans-x1)+(yans-y1)*(yans-y1));
double x=xans,y=yans;
	printf("%.3f %.3f %.3f\n",xans,yans,r);
}

	return 0;
}

C++: /* {{{ Shinobu kawaii */
/*
  ______   __        _                  __                 
.' ____ \ [  |      (_)                [  |                
| (___ \_| | |--.   __   _ .--.   .--.  | |.--.   __   _   
 _.____`.  | .-. | [  | [ `.-. |/ .'`\ \| '/'`\ \[  | | |  
| \____) | | | | |  | |  | | | || \__. ||  \__/ | | \_/ |, 
 \______.'[___]|__][___][___||__]'.__.'[__;.__.'  '.__.'_/ 
                                                           
*/
/* }}} */
/* include {{{ */
#include <cstdio>
#include <cstdlib>
#include <cstring>
#include <cmath>
#include <climits>
#include <iostream>
#include <vector>
#include <string>
#include <sstream>
#include <algorithm>
#include <utility>
#include <set>
#include <map>
#include <stack>
#include <queue>
#include <deque>
#include <functional>
using namespace std;
/* }}} */

// #define int long long

/* cpp template {{{ */
/* short */
#define pb push_back
#define mp make_pair
#define print(x) cout << x << '\n'
#define Fi first
#define Se second

/* REPmacro */
#define REPS(i, a, n) for (int i = (a); i < (n); i++)
#define REP(i, n) for (int i = 0; i < (n); i++)
#define RREP(i, n) for (int i = 1; i <= (n); i++)
#define DEPS(i, a, n) for (int i = (a); i >= n; i--)
#define DEP(i, n) for (int i = (n); i >= 0; i--)

/* typedef */
typedef long long ll;
typedef unsigned long long ull;
typedef vector<int> vi;
typedef vector<vector<int> > vii;
typedef pair<int, int> pii;

/* const */
const int INF = 999999999;
const double EPS = 1e-12;
const int dx[] = {0, 1, 0, -1, 1, -1, 1, -1}, dy[] = {1, 0, -1, 0, 1, -1, -1, 1};

/* func */
inline bool is_uruu(int y) {return (y % 4 == 0 && (y % 100 != 0 || y % 400 == 0));}
inline bool inside(int y, int x, int H, int W) {return (y >= 0 && x >= 0 && y < H && x < W);}

/* }}} */

#define sq(x) ((x) * (x))

signed main()
{
  //cin.tie(0);
  //ios::sync_with_stdio(false);

  int n;
  cin >> n;

  while (n--){
    double x1, y1, x2, y2, x3, y3;
    cin >> x1 >> y1 >> x2 >> y2 >> x3 >> y3;

    double a = 2 * (x1 - x2), b = 2 * (y1 - y2),
           c = 2 * (x1 - x3), d = 2 * (y1 - y3);

    double y = (c * (sq(x1) * sq(y1) - sq(x2) - sq(y2)) - a * (sq(x1) + sq(y1) - sq(x3) - sq(y3))) / (c * b == a * d ? EPS : c * b - a * d);
    double x = (sq(x1) + sq(y1) - sq(x3) - sq(y3) - d * y) / (c == 0 ? EPS : c);
    double r = sqrt(sq(x - x1) + sq(y - y1));
    printf("%.3f %.3f %.3f\n", x, y, r);
  }

  return (0);
}

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

int main(void) {
  int i, n, j, k;
  double x1, y1, x2, y2, x3, y3;
  scanf("%d", &n);
  for(i = 0; i < n; ++i) {
    scanf("%lf%lf%lf%lf%lf%lf", &x1, &y1, &x2, &y2, &x3, &y3);
    double xt1 = (x1 + x2) / 2, xt2 = (x3 + x2) / 2, yt1 = (y1 + y2) / 2, yt2 = (y3 + y2) / 2;
    double t1 = y1 - y2, t2 = y2 - y3;
    double x, y, k1, k2;
    if(!t1) {
      x = xt1;
      k2 = -(x2 - x3) / (y2 - y3);
      y = k2 * (x - xt2) + yt2;
    } else if(!t2) {
      x = xt2;
      k1 = -(x1 - x2) / (y1 - y2);
      y = k1 * (x - xt1) + yt1;
    } else {
      k1 = -(x1 - x2) / (y1 - y2), k2 = -(x2 - x3) / (y2 - y3);
      x = ((k1 * xt1 - k2 * xt2) - (yt1 - yt2)) / (k1 - k2);
      y = k1 * (x - xt1) + yt1;
      //printf("%f %f ", k1, k2);
    }
    double r = sqrt((x - x1) * (x - x1) + (y - y1) * (y - y1));
    //printf("%f %f %f %f\n", xt1, yt1, xt2, yt2);
    printf("%.3f %.3f %.3f\n", x, y, r);
  }
  return 0;
}