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 <bits/stdc++.h>
using namespace std;
typedef long long int ll;
const int INF = 1000000000;
#define REP(i,s,n) for(int i=(int)(s);i<(int)(n);i++)
#define rep(i,n) REP(i, 0, n)
typedef complex<double> Point;
const double EPS = 1.0e-9;
const double PI = acos(-1);
int main(){
    cin.tie(0);
    ios::sync_with_stdio(false);
    int test; cin >> test;
    rep(casenum, test){
        Point a, b, c, m1, m2, d1, d2;
        cin >> a.real() >> a.imag() >> b.real() >> b.imag() >> c.real() >> c.imag();
        m1 = (a + b) / 2.0, m2 = (b + c) / 2.0;//????????¨???????????????, ????????¨????????????
        double s1 = arg(b - a) + PI / 2.0, s2 = arg(c - b) + PI / 2.0;//?????¨??´???????????????
        d1 = polar(1.0, s1), d2 = polar(1.0, s2);
        Point mn = m2 - m1;
        double q = (mn.real() / d1.real() - mn.imag() / d1.imag()) / (d2.real() / d1.real() - d2.imag() / d1.imag());
        q *= -1;
        double x = m2.real() + q * d2.real();
        double y = m2.imag() + q * d2.imag();
        double r = abs(Point(x, y) - a);
        cout << x << ' ' << y << ' ' << r << endl;

        printf("%.3lf %.3lf %.3f\n", x, y, r);
    }
    return 0;
}

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

int main() {
  int n;
  double x1,y1,x2,y2,x3,y3,p,p1,p2,q,q1,q2,r;
  cin >> n;
  for(int i=0;i<n;i++) {
    cin >> x1 >> y1 >> x2 >> y2 >> x3 >> y3;
    p1 = (x2 * x2 - x1 * x1 + y2 * y2 - y1 * y1) * (y3 - y1) - (x3 * x3 - x1 * x1 + y3 * y3 - y1 * y1) * (y2 - y1);
    p2 = 2 * (x1 * y2 - x1 * y3 + x2 * y3 - x2 * y1 + x3 * y1 - x3 * y2);
    p = p1 / p2;
    q1 = (y2 * y2 - y1 * y1 + x2 * x2 - x1 * x1) * (x3 - x1) - (y3 * y3 - y1 * y1 + x3 * x3 - x1 * x1) * (x2 - x1);
    q2 =  2 * (y1 * x2 - y1 * x3 + y2 * x3 - y2 * x1 + y3 * x1 - y3 * x2);
    q = q1 / q2;
    r = sqrt((x1-p) * (x1-p) + (y1-q) * (y1-q) );
    printf("%.3f %.3f %.3f", p, q, r);
  }
}

C++: #include<iostream>
#include<cstdio>
#include<cmath>
using namespace std;

typedef double dbl;

int main() {
	int n;
	cin >> n;

	for (int i = 0; i < n; i++) {
		dbl x1, y1, x2, y2, x3, y3;
		dbl l1, l2, l3;

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

		l1 = sqrt(pow(x3 - x2, 2) + pow(y3 - y2, 2));
		l2 = sqrt(pow(x1 - x3, 2) + pow(y1 - y3, 2));
		l3 = sqrt(pow(x2 - x1, 2) + pow(y2 - y1, 2));

		dbl s, S, r;

		s = (l1 + l2 + l3) / 2;
		S = sqrt(s * (s - l1) * (s - l2) * (s - l3));
		r = (l1 * l2 * l3) / (4 * S);

		dbl A, B, C, D, E, F;

		A = 2 * (x2 - x1); B = 2 * (y2 - y1); C = x2*x2 - x1*x1 + y2*y2 - y1*y1;
		D = 2 * (x3 - x1); E = 2 * (y3 - y1); F = x3*x3 - x1*x1 + y3*y3 - y1*y1;

		dbl ox, oy;

		ox = (C*E - B*F) / (A*E - B*D);
		oy = (A*F - C*D) / (A*E - B*D);

		if (ox == 0) ox = 0;
		if (oy == 0) oy = 0;
		printf("%.3f %.3f %.3f\n", ox, oy, r);
	}
}

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

using namespace std;


int main(){
	int n;
	double x1,x2,x3,y1,y2,y3,ox,oy,r;
	scanf("%d",&n);

	for(int i=0;i<n;i++){
		scanf("%lf %lf %lf %lf %lf %lf",&x1,&y1,&x2,&y2,&x3,&y3);
		ox=((y2-y1)*((y3*y3-y1*y1)+(x3*x3-x1*x1))-(y3-y1)*((y2*y2-y1*y1)+(x2*x2-x1*x1)))/
				(2*((x3-x1)*(y2-y1)-(x2-x1)*(y3-y1)));
		oy=((x1-x2)*ox)/(y2-y1)+((y2*y2-y1*y1)+(x2*x2-x1*x1))/(2*(y2-y1));
		r = sqrt((ox-x1)*(ox-x1)+(oy-y1)*(oy-y1));
		printf("%.3lf %.3lf %.3lf\n",ox,oy,r);
	}
    return 0;
}

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

using namespace std;

int main()
{
    int n;
    cin >> n;
    double x1,y1,x2,y2,x3,y3;
    while(n>0)
    {
        cin >> x1 >> y1 >>x2 >> y2 >> x3 >> y3;
        double s,v1x,v1y,v2x,v2y;
        v1x = y2-y1;
        v1y = x1-x2;

        v2x = y3-y1;
        v2y = x1-x3;
        double detA = v1x*v2y-v1y*v2x;
        double hx = (x2+x1)/2;
        double hy = (y2+y1)/2;
        s = (v2y*hx -v2x*hy)/detA;
        double ox,oy;
        ox = hx + s*v1x;
        oy = hy + s*v1y;
        if(-0.0005<ox&&ox<0)ox = 0;
        if(-0.0005<oy&&oy<0)oy = 0;
        double r = sqrt((x1-ox)*(x1-ox)+(y1-oy)*(y1-oy));
        printf("%.3f %.3f %.3f\n",ox,oy,r);
        --n;
    }
    return 0;
}