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 <complex>
#include <cmath>
#define X real()
#define Y imag()
#define F first
#define S second
#define ML make_pair
#define EPS 1e-10
#define PI acos(-1)
using namespace std;
typedef long double  D;
typedef complex<double> P;
typedef complex<double> V;
typedef pair<P,P> L;


// 内積 (Inner Product) : a・b = |a||b|cosθ 1
D IP(V a, V b) {
	return (a.real() * b.real() + a.imag() * b.imag());
}

// 外積 (Exterior Product) : |a×b| = |a||b|sinθ 2
D EP(V a, V b) {
	return (a.real() * b.imag() - a.imag() * b.real());
}

//交点判定
bool ISC(L l1,L l2){
	V v1,v2;
	v1=l1.S-l1.F;
	v2=l2.S-l2.F;
	if(abs(EP(v1,v2))<EPS)
		return false;
	else
		return true;
}

//　交点の座標
P IS(L l1,L l2){
	P p1,p2,p3,p4;
	p1=l1.F,p2=l1.S,p3=l2.F,p4=l2.S;
	D tmp=(EP(p4-p3,p3-p1)/EP(p4-p3,p2-p1));
	V v1=(tmp,tmp);
	return p1+(p2-p1)*v1;
}
int main(void){
	int n;
	cin >>n;
	for(int j=0;j<n;j++){
		P point[4],tmp1,tmp2;
		for(int i=0;i<3;i++)
			cin >> point[i].X >> point[i].Y;
		L l1,l2;
		tmp1=((point[0]+point[1])/P(2.0,0));
		D angle,r=1.0;
		angle=arg(point[1]-point[0]);
		angle+=PI/2.0;
		tmp2=polar(r,angle);
		l1=ML(tmp1,tmp1+tmp2);

		tmp1=(point[0]+point[2])/P(2.0,0);
		angle=arg(point[2]-point[0]);
		angle+=PI/2.0;
		tmp2=polar(r,angle);
		l2=ML(tmp1,tmp1+tmp2);

		point[3]=IS(l1,l2);
		cout << point[3].X << ' '<< point[3].Y << ' '<< abs(point[3]-point[0]) << endl;
	}
	return 0;
}

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

using namespace std;

int main()
{
	int n;
	scanf("%d", &n);
	
	for (int i  = 0; i < n; i++){
		double x[3], y[3], s[3];
		double l, m, n;
		
		for (int j = 0; j < 3; j++){
			scanf("%lf %lf", &x[j], &y[j]);
			s[j] = x[j] * x[j] + y[j] * y[j];
		}
		
		double x2[2], y2[2], s2[2];
		x2[0] = x[0] - x[1];
		y2[0] = y[0] - y[1];
		s2[0] = s[0] - s[1];
		x2[1] = x[0] - x[2];
		y2[1] = y[0] - y[2];
		s2[1] = s[0] - s[2];
		
		m = - (s2[0] * x2[1] - s2[1] * x2[0]) / (y2[0] * x2[1] - y2[1] * x2[0]);
		l = - (s2[0] * y2[1] - s2[1] * y2[0]) / (x2[0] * y2[1] - x2[1] * y2[0]);
		n = - s[0] - x[0] * l - y[0] * m;
		
		double a,b,r;
		
		a = l / -2;
		b = m / -2;
		r = sqrt(- n - a * a - b * b - l * a - m * b);
		
		printf("%.3lf %.3lf %.3lf\n", a, b, r);
		
		}
	return(0);
}

C++: #include<string>
#include<vector>
#include<iostream>
#include<algorithm>
#include<cstdio>
#include<cstdlib>
#include<sstream>
#include<functional>
#include<map>
#include<set>
#include<cmath>
#include<iomanip>

#define REP(i,s,e) for(int i=int(s);i<=int(e);i++)
#define rep(i,n) for(int i=0;i<int(n);i++)

using namespace std;

int main(){

	int n;


	cin >> n;

	double x1,y1,x2,y2,x3,y3;
	rep(i,n){

	cin >> x1 >> y1 >> x2 >> y2 >> x3 >> y3;

	double a=x2*x2-x1*x1+y2*y2-y1*y1;
	double b=x3*x3-x1*x1+y3*y3-y1*y1;
	double c=4*(x2-x1)*(y3-y1)-4*(x3-x1)*(y2-y1);

	double xp=(2*(y3-y1)*a-2*(y2-y1)*b)/c;
	double yp=(-2*(x3-x1)*a+2*(x2-x1)*b)/c;
	double r=sqrt((xp-x1)*(xp-x1)+(yp-y1)*(yp-y1));

    printf("%.3lf %.3lf %.3lf\n",xp,yp,r);

	}


	return 0;
}