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++: #define _CRT_SECURE_NO_WARNINGS
#include<cstdio>
#include<cstdlib>
#include<cstring>
#include<cmath>
#include<ctime>
#include<cctype>
#include<climits>
#include<iostream>
#include<string>
#include<vector>
#include<map>
#include<list>
#include<queue>
#include<deque>
#include<algorithm>
#include<numeric>
#include<utility>
#include<complex>
#include<memory>
#include<functional>

#define REP(i, n) for(int i = 0;i < n;i++)
#define REPR(i, n) for(int i = n;i >= 0;i--)
#define FOR(i, m, n) for(int i = m;i < n;i++)
#define FORR(i, m, n) for(int i = m;i >= n;i--)
#define SORT(v, n) sort(v, v+n);
#define VSORT(v) sort(v.begin(), v.end());
#define llong long long
#define pb(a) push_back(a)
#define INF 999999999
using namespace std;

typedef vector<int> vi;
typedef vector<long long> vl;
typedef vector<double> vd;
typedef pair<int, int> pii;
typedef pair<long, long> pll;
typedef long long ll;

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


int main(){
	ios::sync_with_stdio(false);

	int n;
	vd x(3), y(3);
	double a1, a2, b1, b2, c1, c2;
	double px, py, r;

	scanf("%d", &n);

	for (; n > 0; n--){
		cin >> x[0] >> y[0] >> x[1] >> y[1] >> x[2] >> y[2];

		a1 = 2 * (x[1] - x[0]);
		b1 = 2 * (y[1] - y[0]);
		c1 = x[0] * x[0] - x[1] * x[1] + y[0] * y[0] - y[1] * y[1];

		a2 = 2 * (x[2] - x[0]);
		b2 = 2 * (y[2] - y[0]);
		c2 = x[0] * x[0] - x[2] * x[2] + y[0] * y[0] - y[2] * y[2];

		px = (b1*c2 - b2*c1) / (a1*b2 - a2*b1);
		py = (c1*a2 - c2*a1) / (a1*b2 - a2*b1);
		r = sqrt((px - x[0])*(px - x[0]) + (py - y[0])*(py - y[0]));

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

}

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

int main ()
{
    int num;
    double x1,y1,x2,y2,x3,y3;

    cin >> num;

    for( int i = 0; i < num; i++ )
    {
        double px = 0, py = 0, r = 0;
        double a, b, c, d, e, f, g;
        cin >> x1 >> y1 >> x2 >> y2 >> x3 >> y3;

        px = ((x1*x1-x3*x3+y1*y1-y3*y3)*(y2-y1)-(x1*x1-x2*x2+y1*y1-y2*y2)*(y3-y1)) / (2*(x2-x1)*(y3-y1)-2*(x3-x1)*(y2-y1));
        
        /*
        a = (x1*x1-x3*x3+y1*y1-y3*y3);
        b = (y2-y1);
        c = (x1*x1-x2*x2+y1*y1-y2*y2);
        d = (y3-y1);
        e = 2*(x2-x1)*(y3-y1);
        f = 2*(x3-x1)*(y2-y1);

        cout << "a: " << a << " b: " << b << " c: " << c << " d: " << d << " e: " << e << " f: " << f << endl;
        g = (a*b-c*d) / (e-f);
        cout << "g: " << g << endl;
        */

        py = ((2*(x1-x2)*px+x2*x2-x1*x1+y2*y2-y1*y1)) / (2*(y2-y1));
        r = (px-x1)*(px-x1) + (py-y1)*(py-y1);

        cout << fixed;
        cout << setprecision(3) << px << " " << py << " " << sqrt(r) << endl;
    }

    return 0;
}

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

int main(){
	int n;
	cin >> n;
	double x[n], y[n], r[n];
	for(int i = 0; i < n; i++){
		double x1, y1, x2, y2, x3, y3;
		double a, b, c, d, e, f;
		cin >> x1 >> y1 >> x2 >> y2 >> x3 >> y3;
		a = 2*(x1-x2);
		b = 2*(y1-y2);
		c = 2*(x2-x3);
		d = 2*(y2-y3);
		e = x1*x1-x2*x2+y1*y1-y2*y2;
		f = x2*x2-x3*x3+y2*y2-y3*y3;
		x[i] = (d*e-b*f)/(a*d-c*b);
		y[i] = (a*f-c*e)/(a*d-b*c);
		r[i] = sqrt((x[i]-x1)*(x[i]-x1)+(y[i]-y1)*(y[i]-y1));
		if((int)floor(r[i]*10000)%10 > 4){
			r[i] = r[i] + 0.001;
		}
	}
	for(int i = 0; i < n; i++){
		cout <<  fixed << setprecision(3) << x[i] << " " << y[i] << " " << r[i] << endl;
	}
}

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

struct Zahyou
{
	float x, y;
};

int main()
{
	int n;
	Zahyou de[4];

	scanf("%d", &n);
	for (int i = 0; i < n; i++)
	{
		for (int j = 1; j < 4; j++)
		{
			scanf("%f %f", &de[j].x, &de[j].y);
		}
		de[0].x = ((de[1].y - de[3].y)*(pow(de[1].y, 2) - pow(de[2].y, 2) + pow(de[1].x, 2) - pow(de[2].x, 2)) + (de[1].y - de[2].y)*(pow(de[1].y, 2) - pow(de[3].y, 2) + pow(de[1].x, 2) - pow(de[3].x, 2))) / (2 * (de[1].y - de[3].y)*(de[1].x - de[2].x) + 2 * (de[1].y - de[2].y)*(de[1].x - de[3].x));
		de[0].y = ((de[1].x - de[3].x)*(pow(de[1].x, 2) - pow(de[2].x, 2) + pow(de[1].y, 2) - pow(de[2].y, 2)) + (de[1].x - de[2].y)*(pow(de[1].x, 2) - pow(de[3].x, 2) + pow(de[1].y, 2) - pow(de[3].y, 2))) / (2 * (de[1].x - de[3].x)*(de[1].y - de[2].y) + 2 * (de[1].x - de[2].x)*(de[1].y - de[3].y));
		
		printf("%.3f %.3f %.3f\n",de[0].x,de[0].y,sqrt(de[0].x+de[0].y));
	}
	return 0;
}