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 <stdio.h>
#include <string>
#include <map>
#include <vector>
#include <set>
#include <iomanip>
#include <fstream>
#include <cstdint>
#include <cmath>
#include <algorithm>
#include <utility>
#include <numeric>
#include <functional>
using namespace std;

constexpr int INF       = 1000000000;/* 1e+9a */
constexpr int MODULO    = 1000000007;

#define int long

#define REP(i,f,n) for(int i=(f); i < (n); ++i)
#define PER(i,f,n) for(int i=(n-1); i >= f; --i)

constexpr int dx[4] = { 1, 0, -1, 0 };
constexpr int dy[4] = { 0, 1, 0, -1 };

//----------------------------------
//----------------------------------

template<typename STL> inline void print_STL(STL c, string ab = ""){
	cout << ab << c[0];
	for(int i = 1; i < c.size(); ++i) cout << ' ' << c[i]; }

template<typename STL> inline void import_STL(STL& c, int n){
	typename STL::value_type tmp;
	for(int i = 0; i < n; ++i){	cin >> tmp; c.push_back(tmp);} }

istream& operator>>(istream& os, pair<double,double>& x)
{
	double tmp;
	os >> tmp;
	x.first = tmp;
	os >> tmp;
	x.second = tmp;
	return os;
}

ostream& operator<<(ostream& os, pair<double,double>& x)
{
	return os << x.first << ' ' << x.second;
}

pair<double, double> operator-(pair<double,double> a, pair<double,double> b)
{
	return {a.first - b.first, a.second - b.second};
}
pair<double, double> operator+(pair<double,double> a, pair<double,double> b)
{
	return {a.first + b.first, a.second + b.second};
}

double operator*(pair<double, double> a, pair<double,double> b)
{
	return a.first * b.first + a.second * b.second;
}
double sq(double a)
{
	return a * a;
}

double round4(double x)
{
	x *= 1000;
	x = (int)(x + 0.5);
	return x / 1000.;
}

signed main()
{
	pair<double,double> a, b, c;
	int n;
	cin >>n;
	for(int i = 0; i < n; ++i)
	{
		cin >> a >> b >> c;
		pair<double, double> va = b-c, vb = c-a;
		/* cout << va <<' ' << vb << '\n'; */
		/* auto m = b + c, n = c + a; */
		/* m = {m.first / 2, m.second/2}; */
		/* n = {n.first / 2, n.second/2}; */
		double norm = va.first * vb.second - va.second * vb.first;
		/* double cx = va * m , cy = vb * n ; */
		double cx = sq(b.first) + sq(b.second) - sq(c.first) - sq(c.second);
		double cy = sq(c.first) + sq(c.second) - sq(a.first) - sq(a.second);
		cx /= 2;
		cy /= 2;
		double sx = cx * vb.second - cy * va.second;
		double sy = va.first * cy - cx * vb.first;
		sx /= norm;
		sy /= norm;

		double r = sqrt(sq(c.first - sx)+ sq(c.second - sy));
		sx = round4(sx);
		sy = round4(sy);
		r = round4(r);
		printf("%.3lf %.3lf %.3lf\n", sx, sy, r);
	}
}

C++: #include <iostream>
#include <cmath>

using namespace std;

#define reep(i, a, n) for(int i = a;i < n; i++)
#define rep(i, n) reep(i, 0, n)

double pow2(double in){
    return in * in;
}

double distance(double x1, double y1, double x2, double y2){
    return sqrt(pow2(y2 - y1) + pow2(x2 - x1));
}

int main(){
    
    int n;
    double x[3], y[3], a, b, cx, cy, r, X[2], Y[2], al, be, cal, ca, sa;
    
    scanf("%d", &n);
    
    rep(i, n){
        
        rep(j, 3){
            scanf("%lf %lf", &x[j], &y[j]);
        }
        
        ca = (pow2(distance(x[0], y[0], x[1], y[1])) 
ツ　ツ　ツ　ツ　ツ　ツ　ツ　ツ　ツ　ツ　ツ　+ pow2(distance(x[1], y[1], x[2], y[2])) 
ツ　ツ　ツ　ツ　ツ　ツ　ツ　ツ　ツ　ツ　ツ　- pow2(distance(x[2], y[2], x[0], y[0])))
ツ　ツ　ツ　ツ　ツ　 / (2.0 * distance(x[0], y[0], x[1], y[1]) * distance(x[1], y[1], x[2], y[2]));
        
        sa = sqrt(1.0 - pow2(ca));
        
        r = distance(x[2], y[2], x[0], y[0]) / sa;
        
        r /= 2.0;
        
        X[0] = x[1] - x[0];
        X[1] = x[2] - x[0];
        Y[0] = y[1] - y[0];
        Y[1] = y[2] - y[0];
        
        al = -(pow2(x[0]) - pow2(x[1]) + pow2(y[0]) - pow2(y[1]));
        be = -(pow2(x[0]) - pow2(x[2]) + pow2(y[0]) - pow2(y[2]));
        
        cal = (X[0] * Y[1] - X[1] * Y[0]) * 2.0;
        
        cx = (Y[1] * al - Y[0] * be) / cal;
        cy = (X[0] * be - X[1] * al) / cal;
        
        printf("%.3lf %.3lf %.3lf\n", cx, cy, r);
        
    }
    
    return 0;
}