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>

double a,b,c,d,e,f,x,y,r;
int n;

double ifof(double a){
	int n = a*10000;
	if(n%10 >= 5)
		n+=10;
	else if(n%10 <= -5)
		n-=10;
	return n/10000.0;
}

double solvex(){
	double k,l;
	k = (c*c)-(a*a)+(d*d)-(b*b)-(2*y*(d-b));
	l = 2*(c-a);
	return k/l;
}

double solvey(){
	double k,l;
	k = ((e-a)*((c*c)-(a*a)+(d*d)-(b*b)))-((c-a)*((e*e)-(a*a)+(f*f)-(b*b)));
	l = 2*(((d-b)*(e-a))-((f-b)*(c-a)));
	return k/l;
}

int main(){
	std::cin >> n;
	for(int i=0; i<n; i++){
		std::cin >> a >> b >> c >> d >> e >> f;
		y = solvey();
		x = solvex();
		r = std::sqrt(((x-a)*(x-a)) + ((y-b)*(y-b)));
		std::printf("%.3f %.3f %.3f\n",ifof(x),ifof(y),ifof(r));
	}
	return 0;
}

C++: #include <iostream>
#include <iomanip>
#include <cmath>
using namespace std;
int main()
{
	double n;
	double x1, x2, x3,y1,y2,y3;
	cin >> n;
	cin >> x1 >> y1 >> x2 >> y2 >> x3 >> y3;
	double px, py, r;
	double A = (x2 - x1)*(y3 - y2) - (y2 - y1)*(x3 - x2);
	px = 0.5*((y3 - y2)*(x2*x2 - x1*x1 + y2*y2 - y1*y1) - (y2 - y1)*(x3*x3 - x2*x2 +                       y3*y3 - y2*y2)) / A;
	py = 0.5*(-(x3 - x2)*(x2*x2 - x1*x1 + y2*y2 - y1*y1) + (x2 - x1)*(x3*x3 - x2*x2 + y3*y3 - y2*y2)) / A;
	double a = px - x1;
	double b = py - y1;
	double r0 = (a*a + b*b);
	double r1 = sqrt(r0);
	cout << fixed << setprecision(10) << px << ' ' << py << ' ' << r1 <<  endl;
}

C++: #include <cstdio>
#include <vector>
#include <cmath>
#include <algorithm>

using namespace std;

#define reep(i,f,n) for(int i=f; i<int(n); ++i)
#define rep(i,n) reep(i,0,n)

typedef vector<int> vi;

int main()
{
	int n;
	scanf("%d", &n);
	rep(i, n){
		double x1, y1, x2, y2, x3, y3;
		scanf("%lf%lf%lf%lf%lf%lf", &x1, &y1, &x2, &y2, &x3, &y3);
		double a1 = 2.0*(x2-x1);
		double b1 = 2.0*(y2-y1);
		double c1 = x1*x1 - x2*x2 + y1*y1 - y2*y2;
		double a2 = 2.0*(x3-x1);
		double b2 = 2.0*(y3-y1);
		double c2 = x1*x1 - x3*x3 + y1*y1 - y3*y3;

		double px = (b1*c2-b2*c1)/(a1*b2-a2*b1);
		double py = (c1*a2-c2*a1)/(a1*b2-a2*b1);
		printf("%.3f %.3f %.3f\n", px, py, sqrt((px-x1)*(px-x1) + (py-y1)*(py-y1)));
	}

	return 0;
}

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

int w(int n)
{
  return n * n;
}

int main()
{
  double x1, y1, x2, y2, x3, y3;
  int n;
  double a, b, c, x, y;
  double px, py, r;

  cin >> n;

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

    a = sqrt(w(x1 - x2) + w(y1 - y2));
    b = sqrt(w(x2 - x3) + w(y2 - y3));
    c = sqrt(w(x3 - x1) + w(y3 - y1));
    px = ((y1 - y3) * (w(y1) - w(y2) + w(x1) - w(x2)) - (y1 - y2) * (w(y1) - w(y3) + w(x1) - w(x3))) / (2 * (y1 - y3) * (x1 - x2) - 2 * (y1 - y2) * (x1 - x3));
    py = ((x1 - x3) * (w(x1) - w(x2) + w(y1) - w(y2)) - (x1 - x2) * (w(x1) - w(x3) + w(y1) - w(y3))) / (2 * (x1 - x3) * (y1 - y2) - 2 * (x1 - x2) * (y1 - y3));
    //r = (a * b * c) / sqrt((a + b + c) * (b + c - a) * (a - b + c) * (a + b - c));
    x = ((a * a) - ((b * b) + (c * c))) / (-2 * b * c);
    y = sqrt(1 - x * x);
    r = a / (2 * y);
    printf("%.3f %.3f %.3f\n", px, py, r);
  }

  return 0;
}

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

using namespace std;

int main()
{
	int n;
	double x[3], y[3], a1, b1, c1, a2, b2, c2, px, py, r;

	cin >> n;

	for(int i=0; i<n; i++)
	{
		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("%.3f %.3f %.3f\n", px, py, r);
	}

	return 0;
}

C++: #include<bits/stdc++.h>
using namespace std;

int main(){

  double x1,y1,x2,y2,x3,y3;
  double px,py;
  int n;

  cin >> n;

  for(int i=0; i<n; i++){
    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));
    cout << px <<" "<< py <<" ";
    printf("%.3f\n", sqrt((px-x1)*(px-x1)+(py-y1)*(py-y1))+0.0005);

  }


  return 0;
}