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 <cstdio>
#include <cmath>

using namespace std;

#define EPS 1e-9

struct P {
	double x, y;
};

double abs(P p) {
	return sqrt(p.x * p.x + p.y * p.y);
}
double dot(P p1, P p2) {
	return p1.x * p2.x + p1.y * p2.y;
}
double xx(double r) {
	return r*r;
}

int main() {
	int n; cin >> n;
	for (int t = 0; t < n; ++t) {
		double x1, x2, x3, y1, y2, y3;
		cin >> x1 >> y1;
		cin >> x2 >> y2;
		cin >> x3 >> y3;

		P a = (P){ x2 - x1, y2 - y1 };
		P b = (P){ x3 - x2, y3 - y2 };
		P c = (P){ x1 - x3, y1 - y3 };

		double R =  abs(a) / (sqrt(1 - xx(dot(b, c) / abs(b) / abs(c))) * 2);
		double l = sqrt( R*R - xx(abs(c)/2) );
		double gx = (x1+x3)/2, gy = (y1+y3)/2;
		P e = (P){ -c.y/abs(c), c.x/abs(c) };
		P eg = (P){ e.x * l, e.y * l };
		P g1 = (P){ gx + eg.x, gy + eg.y };
		P g2 = (P){ gx - eg.x, gy - eg.y };
		if ( abs(xx(x1-g1.x) + xx(y1-g1.y) - R) < EPS ) gx = g1.x, gy = g1.y;
		else gx = g2.x, gy = g2.y;
		printf("%.3f %.3f %.3f\n", gx, gy, R);
	}
}

C++: #include <iostream>
#include <string>
#include <vector>
#include <algorithm>
#include <cmath>
#include <cstdio>
#include <cstring>
using namespace std;

#define FOR(i,a,b) for(long long int i=(a);i<(b);i++)
#define REP(i,n) for(long long int i=0;i<(n);i++)
#define ALL(s) (s).begin(),(s).end()

#define PI 3.14159265358479

typedef long long int ll;
typedef vector<long long int> vi;
typedef vector<long long int>::iterator vit;

void se(double a, double b, double c, double d, double e, double f,double *x,double *y){
	if (a < 0){
		a = -a;
		b = -b;
		c = -c;
	}
	if (b == -0)b = 0;
	if (d < 0){
		d = -d;
		e = -e;
		f = -f;
	}
	cout << a << " " << b << " " << c << " " << d << " " << e << " " << f << "\n";
	if (a == 0){
		*y = c / b;
		*x = (f - e*(*y)) / d;
	}
	else if (b == 0){
		*x = c / a;
		*y = (f - e*(*x)) / d;
	}
	if (d == 0){
		*y = f / e;
		*x = (c - b*(*y)) / a;
	}
	else if (e == 0){
		*x = f / d;
		*y = (c - a*(*x)) / b;
	}
	else if (a != 0 && b != 0 && d != 0 && e != 0){
		*x = (b*f - c*e) / (b*d - a*e);
		*y = (c*d - a*f) / (b*d - a*e);
	}
}


int main(){
	double x1, y1, x2, y2, x3, y3, px, py, r;
	ll n;
	cin >> n;
	REP(i,n){
		cin >> x1 >> y1 >> x2 >> y2 >> x3 >> y3;
		se(2.0*(x1 - x2), 2.0*(y1 - y2),
			pow(x1, 2.0) + pow(y1, 2.0) - pow(x2, 2.0) - pow(y2, 2.0),
			2.0*(x2 - x3), 2.0*(y2 - y3),
			pow(x2, 2.0) + pow(y2, 2.0) - pow(x3, 2.0) - pow(y3, 2.0), &px, &py);
		r = pow(pow(x1 - px, 2.0) + pow(y1 - py, 2.0), 0.5);

		printf("%.3lf %.3lf %.3lf", px, py, r);
	}
}