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
#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\n",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 <iostream>
#include <math.h>
#include <stdio.h>

int main(){

	double x1,y1,x2,y2,x3,y3;
	double a,b,c,x,y;
	double n,px,py,r;
	
	std::cin >> n;
	
	while(n--){
		std::cin >> x1 >> y1 >> x2 >> y2 >> x3 >> y3;
		
		a = sqrt(pow(x2-x1,2) + pow(y2-y1,2));
		b = sqrt(pow(x3-x2,2) + pow(y3-y2,2));
		c = sqrt(pow(x3-x1,2) + pow(y3-y1,2));
		
		x = ((a*a)-((b*b)+(c*c)))/(-2*b*c);
		y = sqrt(1-x*x);
		r = a/(2*y);
		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\n", px, py, r);
	}
}

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 - x1)*(X - x1) + (Y - y1)*(Y - y1));

		//?°???°????¬¬??????????????¨?????\
		if (X > 0)
			X = (int)(X * 1000 + 0.5);
		else X = (int)(X * 1000 - 0.5);

		if (Y>0)
			Y = (int)(Y * 1000 + 0.5);
		else Y = (int)(Y * 1000 - 0.5);

		if (R < 0)
			R = -R;
		R = (int)(R * 1000 + 0.5);

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

	return 0;
}

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

struct Point {
	double x, y;
};

double roundDig(double, int);

int main ()
{
	int num;
	Point a, b, c, p, mb, mc;
	double r;

	scanf("%d", &num);
	
	for (int i=0; i<num; i++) {
		scanf("%lf %lf %lf %lf %lf %lf", &a.x, &a.y, &b.x, &b.y, &c.x, &c.y);
		double A1 = 2 * (b.x - a.x), B1 = 2 * (b.y - a.y), C1 = a.x*a.x - b.x*b.x + a.y*a.y - b.y*b.y,
			   A2 = 2 * (c.x - a.x), B2 = 2 * (c.y - a.y), C2 = a.x*a.x - c.x*c.x + a.y*a.y - c.y*c.y;
		
		p.x = (B1*C1 - B2*C1) / (A1*B2 - A2*B1);
		p.y = (C1*A2 - C2*A1) / (A1*B2 - A2*B1);
		
		mb.x = (a.x + b.x) / 2; mb.y = (a.y + b.y) / 2;
		mc.x = (a.x + c.x) / 2; mc.y = (a.y + c.y) / 2;
		
		r = sqrt((p.x - a.x)*(p.x - a.x) + (p.y - a.y)*(p.x - a.y));
		 
		printf("%.3lf %.3lf %.3lf\n", roundDig(p.x, 4), roundDig(p.y, 4), r);
	}
	
    return 0;
}

double roundDig(double n, int dig)
{
	int multi = pow(10, dig);
	
	return (floor(n*multi + 5) / multi);
}