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 <complex>
#include <vector>
#include <algorithm>
using namespace std;

#define EPS 1.0e-6

const double EPS = 1e-7;
typedef complex<double> P; /* _ */
struct L {                 /* üª */
	P p, q;
	L(P p, P q) : p(p), q(q) {}
};

double cross(P a, P b) { return imag(conj(a)*b); }

// ¼üaÆ¼übÌð_ðvZ·éDæÉð·»èªK{D
P crossPointLL(L a, L b){
	double A = cross(a.q-a.p, b.q-b.p);
	double B = cross(a.q-a.p, a.q-b.p);
	return b.p + B/A * (b.q-b.p);
}

// _pÆ_qÌ¼ñªüðÔ·
L pointBisector(P p, P q) {
	P cen = (p+q)*0.5;
	return L(cen, cen+(q-p)*P(0,1));
}

int main(){
	int n;
	cin>>n;
	double x1, y1, x2, y2, x3, y3;
	while(cin>>x1>>y1>>x2>>y2>>x3>>y3){
		// Cuè@
		P p1 = P(x1, y1);
		P p2 = P(x2, y2);
		P p3 = P(x3, y3);
		L l1 = pointBisector(p1, p2);
		L l2 = pointBisector(p2, p3);
		P cen = crossPointLL(l1, l2);
		double r = abs(p1-cen);

		// Êè@
		double a1 = 2*(x2-x1);
		double b1 = 2*(y2-y1);
		double c1 = x1*x1-x2*x2+y1*y1-y2*y2;
		double a2 = 2*(x3-x1);
		double b2 = 2*(y3-y1);
		double c2 = x1*x1-x3*x3+y1*y1-y3*y3;
		double cx = (b1*c2-b2*c1)/(a1*b2-a2*b1);
		double cy = (c1*a2-c2*a1)/(a1*b2-a2*b1);
		P cen2 = P(cx, cy);
		double r2 = abs(p1-cen2);

		// ÜÆß
		int x1000 = 1000*cen2.real()+0.5;
		int y1000 = 1000*cen2.imag()+0.5;
		int r1000 = 1000*r2+0.5;
		printf("%.3f %.3f %.3f", 1.0*x1000/1000+EPS, 1.0*y1000/1000+EPS, 1.0*r1000/1000+EPS);
		cout<<endl;
	}
	return 0;
}

C++: #include <iostream>
#include <algorithm>
#include <cstdio>
#include <cmath>
#include <string>
#include <cctype>
#include <stack>
#include <queue>
#include <vector>
#include <cstdlib>
#include <list>
#define _USE_MATH_DEFINES
#include <math.h>

using namespace std;

int main() {

	int n;
	double x1, x2, x3, y1, y2, y3;
	double X, Y, R;
	double a, b, c, d;

	cin >> n;

	for (int i = 0; i < n; i++) {
		cin >> x1 >> y1 >> x2 >> y2 >> x3 >> y3;

		a = x2 - x1;
		b = x3 - x1;
		c = y2 - y1;
		d = y3 - y1;
	
		X = 0.5*((a*a*d - b*b*c) + c*d*(d - c)) / (a*d - b*c);
		Y = 0.5*(a*b*(a - b) + (b*c*c - a*d*d)) / (b*c - a*d);
		R = sqrt(X*X + Y*Y);

		X += x1;
		Y += y1;
		

		
		printf("%.3lf %.3lf %.3lf\n", X/1000 , Y /1000, R /1000);
	}

	return 0;
}

C++: #include<iostream>
#include<math.h>
using namespace std;

typedef pair<double,double>vec;

vec operator + (vec v1,vec v2){
    return make_pair(v1.first+v2.first,v1.second+v2.second);
}

vec operator - (vec v1,vec v2){
    return make_pair(v1.first-v2.first,v1.second-v2.second);
}

vec operator * (double v,vec v2){
    return make_pair(v*v2.first,v*v2.second);
}

vec operator / (vec v1,double d){
    return make_pair(v1.first/d,v1.second/d);
}

int norm2(vec v1,vec v2){
    return (v1-v2).first*(v1-v2).first+(v1-v2).second*(v1-v2).second;
}

int main(){
    double x1,x2,x3,y1,y2,y3,n,r;
    cin>>n;
    while(n--){
        cin>>x1>>y1>>x2>>y2>>x3>>y3;
        vec A = make_pair(x1,y1);
        vec B = make_pair(x2,y2);
        vec C = make_pair(x3,y3);
        double a2,b2,c2,a,b,c,cosA,cosB,cosC,sinA,sinB,sinC,cos2A,cos2B,cos2C,sin2A,sin2B,sin2C;
        a2=norm2(B,C);
        b2=norm2(A,C);
        c2=norm2(A,B);
        a=sqrt(a2);
        b=sqrt(b2);
        c=sqrt(c2);
        cosA=(b2+c2-a2)/(2*b*c);
        cosB=(a2+c2-b2)/(2*c*a);
        cosC=(b2+a2-c2)/(2*b*a);
        sinA=sqrt(1-cosA*cosA);
        sinB=sqrt(1-cosB*cosB);
        sinC=sqrt(1-cosC*cosC);
        r=(a/sinA)/2;
        cos2A=cosA*cosA-sinA*sinA;
        cos2B=cosB*cosB-sinB*sinB;
        cos2C=cosC*cosC-sinC*sinC;
        sin2A=2*sinA*cosA;
        sin2B=2*sinB*cosB;
        sin2C=2*sinC*cosC;
        
        vec v=(sin2A*A+sin2B*B+sin2C*C )   /    (sin2A+sin2B+sin2C);
        printf("%.3f %.3f %.3f\n",v.first,v.second,r);
    }
    
}