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++: /*
NOTE :
*min_element(.begin(),.end())
*max_element(.begin(),.end())
priority_queue<> pq
 push()  pop() size()  top()
map<>
 find() begin() end() insert(map<>::value_type())
pair<>
sort(.begin(), .end())
sort(arr, arr+N)
sort(a, a+N, greater<int>())
binary_search(vc.begin(), vc.end(), x)  //binary_search???true, false?????????
vector<int>::iterator lit = lower_bound(vc.begin(), vc.end(), x);
  lower_bound?????????????????????"??\???"????????????????????????????????????????????¬???????????????
vector<int>::iterator uit = upper_bound(vc.begin(), vc.end(), x);
  upper_bound????????????????????????"?¶???????"?????????????????????????????????????????¬???????????????
*/
#include <iostream>
#include <cstdio>
#include <climits>
#include <cmath>
#include <cassert>
#include <algorithm>
#include <valarray>
#include <utility>
#include <vector>
#include <string>
#include <stack>
#include <queue>
#include <map>
#include <set>

#define MAX 100
#define INF 1<<20
#define LLINF 10e12 // 1<<31 // 2^31
#define REP(i,n) for(int i=0;i<n;i++)
#define REP2(i,a,n) for(int i=(a);i<(n);i++)
#define SET(a,c) memset(a,c,sizeof a)
#define FOR(i,c) for(__typeof((c).begin())i=(c).begin();i!=(c).end();++i)
#define FOREACH(i,c) for(auto (i) : (c))
#define BIT(i,j) ((i)>>(j))&1
#define ALL(o) (o).begin(), (o).end()
#define ERASE(o) (o).erase(unique(ALL((o))), (o).end());

using namespace std;
typedef long long ll;
typedef valarray<int> array_t;
/////
template <class T>
void printMartix(valarray<valarray<T> > &A)
{
  int n = A.size();
  int m = A[0].size();
  REP(i,n){{REP(j,n) cout << A[i][j] << " ";} cout << endl;}
  cout << endl;
}

template <class T>
void printArray(valarray<T> &A)
{
  int n = A.size();
  REP(i,n) cout << A[i] << " ";
  cout << endl << endl;
}

template <class T>
bool solution(valarray<valarray<T> > &A, valarray<T> &b)
{
  int n = A.size();
  REP(i,n)
  {
    T a;
    //printMartix(A);
    //printArray(b);
    REP2(u,i,n)
    {
      a = A[u][i];
      if(a == 0) continue;
      else
      {
        if(u != i)
        {
          swap(A[i],A[u]);
          swap(b[i],b[u]);
        }
        break;
      }
      if(u == n-1) return false;
    }
    A[i] /= (1.0 * a);
    b[i] /= (1.0 * a);
    REP(j,n)
    {
      if(j == i) continue;
      b[j] -= b[i] * A[j][i];
      A[j] -= A[i] * A[j][i];
    }
    //printMartix(A);
    //printArray(b);
  }
  return true;
}

/////
int main()
{
  cin.tie(0);
  ios::sync_with_stdio(false);
  // FROM HERE
  int n; cin >> n;
  REP(u,n)
  {
    double x[3], y[3]; REP(i,3) cin >> x[i] >> y[i];
    valarray<valarray<double> > A(valarray<double>(0.0,3),3);
    valarray<double> b(0.0,3);
    REP(i,3)
    {
      A[i][0] = x[i];
      A[i][1] = y[i];
      A[i][2] = 1;
      b[i] = -(x[i]*x[i] + y[i]*y[i]);
    }
    solution(A,b);
    double cx = -b[0] * 0.5;
    double cy = -b[1] * 0.5;
    double r = sqrt((x[0]-cx)*(x[0]-cx)+(y[0]-cy)*(y[0]-cy));
    printf("%.3lf %.3lf %.3lf\n",cx,cy,r);
  }
  return 0;
}

C++: #include <iostream>
#include <cmath>
#include <algorithm>
#include <string>
#include <stdio.h>
using namespace std;
int main(){
    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;
    double x,y,r1,r2,r3;
    double a,b,c,d,e,f;
    a=2*x1-2*x2;
    b=2*y1-2*y2;
    c=x1*x1-x2*x2+y1*y1-y2*y2;
    d=2*x2-2*x3;
    e=2*y2-2*y3;
    f=x2*x2-x3*x3+y2*y2-y3*y3;
    y=(a*f-c*d)/(a*e-b*d);
        if(a==0)break;
        x=(c-b*y)/a;
        
    r1=sqrt((x1-x)*(x1-x)+(y1-y)*(y1-y));
    r2=sqrt((x2-x)*(x2-x)+(y2-y)*(y2-y));
    r3=sqrt((x3-x)*(x3-x)+(y3-y)*(y3-y));
    
    printf("%.3f %.3f %.3f\n",x,y,r1);
}
}

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

double marume( double x ){
	long long t = x * 1000 + 0.5;
	return t/1000.0;
}

int main(){
	int n;
	double tx, ty, x1, y1, x2, y2;
	
	cin >> n;
	while(n--){
		cin >> tx >> ty >> x1 >> y1 >> x2 >> y2;
		x1 -= tx; y1 -= ty;
		x2 -= tx; y2 -= ty;
		
		double dist1 = x1 * x1 + y1 * y1;
		double dist2 = x2 * x2 + y2 * y2;
		x1 *= 2; y1 *= 2;
		y1 *= 2; y2 *= 2;
		
		double detA = x1 * y2 - x2 * y1;
		double detX = dist1 * y2 - y1 * dist2;
		double detY = x1 * dist2 - dist1 * x1;
		double x = detX / detA;
		double y = detY / detA;
		double r = hypot(x, y);
		
		//x = marume(x);
		//y = marume(y);
		//r = marume(r);
		printf("%.3f %.3f %.3f\n", x, y, r);
	}
	return 0;
}