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<cmath>
#include<iomanip>
using namespace std;

int main(){
  double x1,x2,x3,y1,y2,y3,x,n;

  cin >> n;
  int i=0;
  while(i < n){
    cin >> x1 >> y1 >> x2 >> y2 >> x3 >> y3;
    double sina,R,BC = sqrt((x2-x3)*(x2-x3)+(y2-y3)*(y2-y3)),p,q;
    sina = ((x2-x1)*(x3-x1) + (y2-y1)*(y3-y1)) / sqrt(((x2-x1)*(x2-x1)+(y2-y1)*(y2-y1))*((x3-x1)*(x3-x1)+(y3-y1)*(y3-y1)));

    p = ((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));
    q = ((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 = BC/(2*sina);

    cout << setprecision(4) << p << " " << setprecision(4) << q << " " << setprecision(4) << R << endl;
    i++;
  }
}

C++: #include <cstdio>
#include <cstdlib>
#include <cstring>
#include <cmath>
#include <ctime>
#include <cassert>
#include <iostream>
#include <cctype>
#include <sstream>
#include <string>
#include <list>
#include <vector>
#include <queue>
#include <set>
#include <map>
#include <utility>
#include <numeric>
#include <algorithm>
#include <bitset>
#include <complex>
#include <fstream>
using namespace std;
typedef long long ll;
const double EPS = 1e-9;
typedef vector<int> vint;
typedef pair<int, int> pint;
#define rep(i, n) REP(i, 0, n)
#define ALL(v) v.begin(), v.end()
#define MSG(a) cout << #a << " " << a << endl;
#define REP(i, x, n) for(int i = x; i < n; i++)
template<class T> T RoundOff(T a){ return int(a+.5-(a<0)); }
template<class T, class C> void chmax(T& a, C b){ if(a < b) a = b; }
template<class T, class C> void chmin(T& a, C b){ if(b < a) a = b; }
template<class T, class C> pair<T, C> mp(T a, C b){ return make_pair(a, b); }


struct P{ double x, y; };


int main()
{
	int n;
	cin >> n;
	
	rep(i, n)
	{
		vector<P> v(3);

		rep(i, 3)
			cin >> v[i].x >> v[i].y;

		double a = v[0].x - v[1].x;
		double b = v[0].y - v[1].y;
		double c = v[1].x - v[2].x;
		double d = v[1].y - v[2].y;

		double A = pow(v[1].x, 2.0) - pow(v[0].x, 2.0) + pow(v[1].y, 2.0) + pow(v[0].y, 2.0);
		double B = pow(v[2].x, 2.0) - pow(v[1].x, 2.0) + pow(v[2].y, 2.0) + pow(v[1].y, 2.0);

		double acbd = a * d - b * c;

		double x = -(A * d - B * b) / acbd / 2;
		double y = -(A *-c + B * a) / acbd / 2;

		double r = sqrt(pow(x - v[0].x, 2.0) + pow(y - v[0].y, 2.0));


		printf("%.3f %.3f %.3f\n", x, y, r);
	}
}

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

int main(){
  int n;
  double a,b,c,d,e,f,x,y,r;
  double x1,y1,x2,y2,x3,y3;

  std::cin >> n;

  for(int i=0;i<n;i++){
    std::cin >> x1>>y1>>x2>>y2>>x3>>y3;
    a = 2*(x1-x2);
    b = 2*(y1-y2);
    c = +(x1*x1-x2*x2)+(y1*y1-y2*y2);
    d = 2*(x2-x3);
    e = 2*(y2-y3);
    f = +(x2*x2-x3*x3)+(y2*y2-y3*y3);

    x = (double)(c*e-b*f)/(a*e-b*d);
    y = (double)(a*f-c*d)/(a*e-b*d);

    if(x == 0){x = 0;}
    if(y == 0){y = 0;}

    r = sqrt((x-x1)*(x-x1)+(y-y1)*(y-y1));

    printf("%.3f %.3f %.3f\n",x,y,r);
  }
}

C++: 
#include <iostream>
#include <cstdlib>
#include <cstdio>
#include <cmath>
#include <stack>
#include <cctype>
#include <complex>
#include <vector>
#include <algorithm>

using namespace std;


bool solve(){
	complex<double> Ans;
	complex<double> P[3];
	for(int i=0;i<3;i++){
		cin>> P[i].real()>> P[i].imag();
	}
	complex<double> T[2];
	complex<double> K[2];
	for(int i=0;i<2;i++){
		T[i].real() = (P[i].real() + P[i+1].real()) / 2;
		T[i].imag() = (P[i].imag() + P[i+1].imag()) / 2;
		complex<double> N;
		N = (P[i+1]-P[i])/abs(P[i+1]-P[i]);
		K[i].real() =  N.imag();
		K[i].imag() = -N.real();
	}
	double a = (T[1]-T[0]).real();
	double b = (T[1]-T[0]).imag();
	double x0 = K[0].real();
	double y0 = K[0].imag();
	double x1 = K[1].real();
	double y1 = K[1].imag();
	double m = ( a * y0 - b * x0 ) / ( x0 * y1 - x1 * y0 );
	K[1] *= m;
	Ans = K[1] + T[1];

	printf("%.3f %.3f %.3f", Ans.real(), Ans.imag(), abs(Ans-P[0]));
	printf("\n");
	
	return true;
}

int main(){
	cout.setf(ios::fixed);
	cout.precision(5);
	int n;
	cin>> n;
	for(int i=0;i<n;i++){
		solve();
	}
	return 0;
}