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<stdio.h>
#include<math.h>

int FLG = 0;

typedef struct{
	double x,y;
}POINT;
	
POINT point(POINT p1,POINT p2);
double incl(POINT p1,POINT p2,int);
double cept(double x,double y,double a);

int main(){
	POINT p1,p2,p3,lp1,lp2;
	int n;
	double la1,la2,lb1,lb2;
	double x,y,r,tmp;
	
	scanf("%d",&n);	
	
	while(n>0){
	scanf("%lf %lf %lf %lf %lf %lf",&p1.x,&p1.y,&p2.x,&p2.y,&p3.x,&p3.y);
	
	lp1 = point(p1,p2);
	la1 = incl(p1,p2,1);
	lb1 = cept(lp1.x,lp1.y,la1);
	
	lp2 = point(p1,p3);
	la2 = incl(p1,p3,2);
	lb2 = cept(lp2.x,lp2.y,la2);
	
	if(FLG == 0){
		x = -1*(lb1-lb2)/(la1-la2);
		y = la1*x+lb1;
		tmp = ((x - p1.x)*(x - p1.x))+((y - p1.y)*(y - p1.y));
		r = sqrt(tmp);
	}
	
	
	//la1が無限
	else if(FLG == 1){
		
		x = lp1.x;
		y = la2 * x + lb2;
		tmp = ((x - p1.x)*(x - p1.x))+((y - p1.y)*(y - p1.y));
		r = sqrt(tmp);		
		
	}
	
	else if(FLG == 2){
		
		x = lp2.x;
		y = la1 * x + lb1;
		tmp = ((x - p1.x)*(x - p1.x))+((y - p1.y)*(y - p1.y));
		r = sqrt(tmp);		
		
	}
	
	
	
	printf("%.3f %.3f %.3f\n",x,y,r);
	
	n--;
	
	}
	
	return 0;
}

//中点座標
POINT point(POINT p1,POINT p2){
	POINT P;
	
	P.x = (p1.x + p2.x)/2;
	P.y = (p1.y + p2.y)/2;
	
	return (P);
}

//傾き
double incl(POINT p1,POINT p2,int plus){
	double a;
	
	double tmp;
	
	tmp = p2.x - p1.x;
	
	if(tmp != 0 ) a = (p2.y - p1.y)/tmp;
	
	else return 0;
		
	if(a==0) FLG += plus;
	else{
	a = -1*(1/a);
	}
	
	return a;
}

//切片
double cept(double x,double y,double a){
	double b;
	
	b = y-(a*x);
	
	return (b);
}

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

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

	while (t--) {
		double x1, y1, x2, y2, x3, y3;
		cin >> x1 >> y1 >> x2 >> y2 >> x3 >> y3;

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

		double px = (c*d - a*f) / (b*d - a*e);
		double py = (c*e - b*f) / (a*e - d*b);

		double r = sqrt((px - x1)*(px - x1) + 
			(py - y1)*(py - y1));

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

	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), roundDig(r, 4));
	}
	
    return 0;
}

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

C++: #include<bits/stdc++.h>
using namespace std;
 
#define REP(i,s,n) for(int i=s;i<n;++i)
#define rep(i,n) REP(i,0,n)
#define SORT(c) sort((c).begin(),(c).end())
#define IINF INT_MAX
#define LLINF LLONG_MAX
 
typedef long long ll;
typedef pair<int, int> ii;
 
int main(){

	int n;
	cin >> n;
	rep(i, n){
		double x1, y1, x2, y2, x3, y3;
		cin >> x1 >> y1 >> x2 >> y2 >> x3 >> y3;
		double vx21, vx31, vy21, vy31, tmp1, tmp2;
		vx21 = (x1 - x2);
		vx31 = (x1 - x3);
		vy21 = (y1 - y2);
		vy31 = (y1 - y3);
		tmp1 = x1 * x1 + y1 * y1 - x2 * x2 - y2 * y2;
		tmp2 = x1 * x1 + y1 * y1 - x3 * x3 - y3 * y3;
		
		double x, y, r;
		x = -(vy21 * tmp2 - vy31 * tmp1) / (2.0 * (vy31 * vx21 - vy21 * vx31));
		y = -(vx21 * tmp2 - vx31 * tmp1) / (2.0 * (vx31 * vy21 - vx21 * vy31));
		r = sqrt((x1 - x) * (x1 - x) + (y1 - y) * (y1 - y));
		
		printf("%.3lf %.3lf %.3lf\n", x, y, r);
		
	}
 
	return 0;
}