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 <cmath>
#include <cstdio>

using namespace std;

long double sisya(long double a) {
	a *= 1000.0;
	if (a-(int)a >= 0.5) {
		a += 1.0;
	}
	a /= 1000.0;
	return a; 
}

int main() {
	int n;
	cin >> n;
	for (int i = 0; i < n; i++) {
		long double x1, y1, x2, y2, x3, y3;
		cin >> x1 >> y1 >> x2 >> y2 >> x3 >> y3; 
		long double a, b, c;
		a = sqrt((x3-x2)*(x3-x2)+(y3-y2)*(y3-y2));
		b = sqrt((x1-x3)*(x1-x3)+(y1-y3)*(y1-y3));
		c = sqrt((x2-x1)*(x2-x1)+(y2-y1)*(y2-y1));
		long double s = (a+b+c)/2.0;
		long double S = sqrt(s*(s-a)*(s-b)*(s-c));
		long double p1, p2, pr;
		p1 = (a*a*(b*b+c*c-a*a)*x1+b*b*(c*c+a*a-b*b)*x2+c*c*(a*a+b*b-c*c)*x3)/(16.0*S*S);
		p2 = (a*a*(b*b+c*c-a*a)*y1+b*b*(c*c+a*a-b*b)*y2+c*c*(a*a+b*b-c*c)*y3)/(16.0*S*S);
		pr = (a*b*c)/sqrt((a+b+c)*(-a+b+c)*(a-b+c)*(a+b-c));
		p1 = sisya(p1);
		p2 = sisya(p2);
		pr = sisya(pr);
		printf("%.3f %.3f %.3f\n", p1, p2, pr);
	}
	return 0;
}

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

#define N 10000
#define INF 200000000

int main()
{
    int n;
    vector<double> x(3), y(3), x2(3), y2(3);
    cin >> n;

    for(int p=0; p<n; p++)
    {
        cin >> x[0] >> y[0] >> x[1] >> y[1] >> x[2] >> y[2];
        for(int i=0; i<3; i++) { x2[i] = x[i]*x[i]; y2[i] = y[i]*y[i]; }

        double a, b, c, a2, b2, c2;
        a2 = abs((x[2]-x[1])*(x[2]-x[1]) + (y[2]-y[1])*(y[2]-y[1]));
        b2 = abs((x[0]-x[2])*(x[0]-x[2]) + (y[0]-y[2])*(y[0]-y[2]));
        c2 = abs((x[1]-x[0])*(x[1]-x[0]) + (y[1]-y[0])*(y[1]-y[0]));
        a = sqrt(a2); b = sqrt(b2); c = sqrt(c2);

        double s, S2;
        s = (a + b + c) / 2;
        S2 = s * (s-a) * (s-b) * (s-c);

        double cx, cy;
        cx = (a2*(b2+c2-a2)*x[0] + b2*(c2+a2-b2)*x[1] + c2*(a2+b2-c2)*x[2]) / (16 * S2);
        cy = (a2*(b2+c2-a2)*y[0] + b2*(c2+a2-b2)*y[1] + c2*(a2+b2-c2)*y[2]) / (16 * S2);

        cout << setprecision(3) << fixed <<
            cx << " " << cy << " " << sqrt(abs((cx-x[0])*(cx-x[0])+(cy-y[0])*(cy-y[0]))) << endl;
    }
}

C++: #include <iostream>
#include <cmath>
#include <cstdio>
#define MAX_N 20
using namespace std;

void swap(double &x,double &y){
	double t;
	t=x;
	x=y;
	y=t;
}

double cut4(double x){
	double temp=x*pow(10,3);
	temp=double(int(temp+0.5));
	return temp*pow(10,-3);
}

int main(){
	int n;
	double x1,x2,x3,y1,y2,y3,px,py;
	double a,b,c,d,r;
	cin>>n;
	for(int i=0;i<n;i++){
		cin>>x1>>y1>>x2>>y2>>x3>>y3;
		if(x1==x2){
			swap(x2,x3);
			swap(y2,y3);
		}else if(x2==x3){
			swap(x1,x2);
			swap(y1,y2);
		}
		a=(y2-y1)/(x2-x1);
		c=(y3-y2)/(x3-x2);
		if(a&&c){
			a=-1/a;
			c=-1/c;
			b=(y1+y2)/2-a*(x1+x2)/2;
			d=(y2+y3)/2-c*(x2+x3)/2;
			px=(b-d)/(c-a);
			py=(b*c-a*d)/(c-a);
		}else if(!a){
			c=-1/c;
			d=(y2+y3)/2-c*(x2+x3)/2;
			px=(x1+x2)/2;
			py=c*(x1+x2)/2+d;
		}else if(!c){
			a=-1/a;
			b=(y1+y2)/2-a*(x1+x2)/2;
			px=(x2+x3)/2;
			py=a*(x2+x3)/2+b;
		}

		r=sqrt((px-x1)*(px-x1)+(py-y1)*(py-y1));
		px=(px==0?0.000:px);
		py=(py==0?0.000:px);
		printf("%.3lf %.3lf %.3lf\n",cut4(px),cut4(py),cut4(r));
	}
	return 0;
}

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

using namespace std;

int main(){
	int n;
	double x1, y1, x2, y2, x3, y3;
	double x, y, r;
	double a1, a2, b1, b2, c1, c2;

	cin >> n;
	while (n--){
		cin >> x1 >> y1 >> x2 >> y2 >> x3 >> y3;

		a1 = 2 * (x2 - x1);
		b1 = 2 * (y2 - y1);
		c1 = x1*x1 - x2*x2 + y1*y1 - y2*y2;

		a2 = 2 * (x3 - x1);
		b2 = 2 * (y3 - y1);
		c2 = x1*x1 - x3*x3 + y1*y1 - y3*y3;

		x = (b1*c2 - b2*c1) / (a1*b2 - a2*b1);
		y = (c1*a2 - c2*a1) / (a1*b2 - a2*b1);

		r = hypot(x - x1, y - y1);

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

	return 0;
}

C++: #include<iostream>
#include<math.h>
#include<vector>
#include<algorithm>
#include<cstdio>
#include<cmath>
using namespace std;

int main()
{
   int n;
   cin>>n;
   while(n--){
       double x1,x2,x3,y1,y2,y3;
       double px,py,r;
       scanf("%lf%lf%lf%lf%lf%lf",&x1,&y1,&x2,&y2,&x3,&y3);
       double a1=(x2*x2+y2*y2-x1*x1-y1*y1)*(y3-y1);
       double b1 =(x3*x3+y3*y3-x1*x1-y1*y1)*(y2-y1);
        double a2 =(x3*x3+y3*y3-x1*x1-y1*y1)*(x2-x1);
        double b2 =(x2*x2+y2*y2-x1*x1-y1*y1)*(x3-x1);
        double c = (x2-x1)*(y3-y1)-(y2-y1)*(x3-x1);
        px=(a1-b1)/c/2;
        py=(a2-b2)/c/2;
        r = sqrt((px-x1)*(px-x1)+(py-y1)*(py-y1));
        printf("%.3f %.3f %.3f\n",px,py,r);
   }
    return 0;
}