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 <stdio.h>
#include <string.h>
#include <math.h>
#include <algorithm>
#include <stdlib.h>

using namespace std;
double a, b, c, d, e, f;
double x, y;


void function(){
	if(c/b == f/e){
		x = 0;
		y = c/b;
	}else if(c/a == f/d){
		y = 0;
		x = c/a;
	}else{
		y = (c*d - a*f)/(d*b - a*e);
		x = (c - b*y)/a;
	}
	return;
}


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

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

		a = 2*(x2 - x1);
		b = 2*(y2 - y1);
		c = (x2 - x1)*(x1 + x2) + (y2 - y1)*(y1 + y2);

		d = 2*(x3 - x1);
		e = 2*(y3 - y1);
		f = (x3 - x1)*(x3 + x1) + (x3 - x1)*(x1 + x3);

		function();
		double r;
		r = sqrt((x - x1)*(x - x1) + (y - y1)*(y - y1));

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

C++: #define _CRT_SECURE_NO_WARNINGS
#define M_PI 3.14159265358979
#include <iostream>
#include <stdio.h>
#include <string>
#include <math.h>
#include<iomanip>
#include<vector>
#include<cmath>
#include <algorithm>

using namespace std;

double hankei(double z1,double z2,double dx,double dy){
	 
	double r = sqrt((dx - z1)*(dx - z1) + (dy - z2)*(dy - z2));
	return r;
}


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

		px = ((y1 - y3)*(y1*y1 - y2*y2 + x1*x1 - x2*x2) - (y1 - y2)*(y1 *y1 - y3*y3 + x1 *x1 - x3 *x3)) / (2 *(y1 - y3)*(x1 - x2) - 2 * (y1 - y2)*(x1 - x3));
		py = ((x1 - x3)*(x1*x1 - x2*x2 + y1*y1 - y2*y2) - (x1 - x2)*(x1 *x1 - x3*x3 + y1 *y1 - y3 *y3)) / (2 *(x1 - x3)*(y1 - y2) - 2 * (x1 - x2)*(y1 - y3));

		printf("%.3f %.3f %.3f ",floor(px * 1000 + 0.5) / 1000,floor(py * 1000 + 0.5) / 1000 ,floor(hankei(x1, y1, px, py) * 1000 + 0.5) / 1000);
	}
	
	return 0;
}

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

int main(){
    int n;
    double x1, y1, x2, y2, x3, y3, det2, A, B, X, Y, R;
    scanf("%d", &n);
    while(n--){
        scanf("%lf %lf %lf %lf %lf %lf",
               &x1, &y1, &x2, &y2, &x3, &y3);
        det2 = 2*((x1-x2)*(y1-y3)-(y1-y2)*(x1-x3));
        A = x1*x1-x2*x2+y1*y1-y2*y2;
        B = x1*x1-x3*x3+y1*y1-y3*y3;
        X = ((y1-y3)*A-(y1-y2)*B)/det2;
        Y = ((x1-x2)*B-(x1-x3)*A)/det2;
        R = sqrt((X-x1)*(X-x1)+(Y-y1)*(Y-y1));
        printf("%.3lf %.3lf %.3lf\n", 
                X, Y, R);
    }
    return 0;
}

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

#define SQ(x) ((x)*(x))

using namespace std;

int main(void)
{
	int n = 0;
	cin >> n;
	
	for(int i = 0; i < n; i++){
		double x1 = 0.0, y1 = 0.0;
		double x2 = 0.0, y2 = 0.0;
		double x3 = 0.0, y3 = 0.0;
		cin >> x1 >> y1 >> x2 >> y2 >> x3 >> y3;
		
		double a = x1 - x2;
		double b = y1 - y2;
		double c = SQ(x2) + SQ(y2) - SQ(x1) - SQ(y1);
		double d = x2 - x3;
		double e = y2 - y3;
		double f = SQ(x3) + SQ(y3) - SQ(x2) - SQ(y2);
		
		double l = (c * e - b * f) / (a * e - b * d);
		double m = (a * f - c * d) / (a * e - b * d);
		double n = -1.0 * (SQ(x1) + SQ(y1) + l * x1 + m * y1);
		
		double centerX = l / -2.0;
		double centerY = m / -2.0;
		double radius = sqrt( SQ(l) / 4.0 + SQ(m) / 4.0 - n );
		
		cout.precision(3);
		cout << fixed << centerX << " " << centerY << " " << radius << endl;
	}
	
	return 0;
}

C++: #include<iostream>
#include<iomanip>
#include<string>
#include<algorithm>
#include<functional>
#include<vector>
#include<math.h>

using namespace std;

typedef long long int lli;

int main() {
	int n;
	double xy[3][3],x,y;
	double a, b, c, d, e, f, radius;
	cin >> n;
	for (int i = 0; i < n; i++) {
		for (int j = 0; j < 3; j++) {
			for (int k = 0; k < 2; k++) {
				cin >> xy[j][k];
			}
		}
		a = -2 * (xy[0][0]-xy[1][0]);
		b = -2 * (xy[0][1] - xy[1][1]);
		c = -1 * (pow(xy[0][0], 2) + pow(xy[0][1], 2)) + pow(xy[1][0], 2) + pow(xy[1][1], 2);
		d = -2 * (xy[0][0] - xy[2][0]);
		e = -2 * (xy[0][1] - xy[2][1]);
		f = -1 * (pow(xy[0][0], 2) + pow(xy[0][1], 2)) + pow(xy[2][0], 2) + pow(xy[2][1], 2);
		y = (a*f - c*d) / (a*e - b*d);
		x = (c*e - b*f) / (a*e - b*d);
		if (x == 0) x = 0;
		if (y == 0) y = 0;
		radius =sqrt(pow((x-xy[0][0]),2)+pow((y-xy[0][1]),2));

		cout << fixed << setprecision(3) << x << " " << y << " "<< radius <<endl;
	}
	return 0;
}