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++: /*
A1＝2(X2?X1)
B1＝2(Y2?Y1)
C1＝X12?X22＋Y12?Y22
A2＝2(X3?X1)
B2＝2(Y3?Y1)
C2＝X12?X32＋Y12?Y32

X＝(B1C2?B2C1)/(A1B2?A2B1)
Y＝(C1A2?C2A1)/(A1B2?A2B1)
*/
#include <fstream>
#include <iostream>
#include <math.h>
#include <vector>
#include <queue>
#include <utility>
#include <algorithm>
#define PI 3.14159265
using namespace std;

int main() {
  // ifstream cin("../test.txt");
  int n;
  cin >> n;
  while (n--) {
    double x1,y1,x2,y2,x3,y3;
    cin >> x1 >> y1 >> x2 >> y2 >> x3 >> y3;
    double a1 = 2 * (x2 - x1);
    double b1 = 2 * (y2 - y1);
    double c1 = x1 * x1 - x2 * x2 + y1 * y1 - y2 * y2;
    double a2 = 2 * (x3 - x1);
    double b2 = 2 * (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);

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

    px += 0.0005;
    py += 0.0005;
    // r  += 0.0004;
    printf("%.3f %.3f %.3f\n", px, py, r);
  }
}

C++: #include<iostream>
#include<iomanip>
#include<cmath>
int main()
{
	int n;
	std::cin >> n;
	double**result = new double*[n];
	for(int i = 0; i < n; i++)
	{
		result[i] = new double[3];
		double x1, y1, x2, y2, x3, y3;
		std::cin >> x1 >> y1 >> x2 >> y2 >> x3 >> y3;
		double dx12 = x1 - x2, dx23 = x2 - x3, dx31 = x3 - x1, dy12 = y1 - y2, dy23 = y2 - y3, dy31 = y3 - y1;
		result[i][0] = (x1 * x1 * dy23 + x2 * x2 * dy31 + x3 * x3 * dy12 - dy12 * dy23 * dy31) / (x1 * dy23 + x2 * dy31 + x3 * dy12) / 2;
		result[i][1] = (y1 * y1 * dx23 + y2 * y2 * dx31 + y3 * y3 * dx12 - dx12 * dx23 * dx31) / (y1 * dx23 + y2 * dx31 + y3 * dx12) / 2;
		double dx = result[i][0] - x1, dy = result[i][1] - y1;
		result[i][2] = sqrt(dx * dx + dy * dy);
	}
	std::cout << std::fixed << std::setprecision(3);
	for(int i = 0; i < n; i++)
	{
		std::cout << result[i][0] << ' ' << result[i][1] << ' ' << result[i][2] << std::endl;
		delete[]result[i];
	}
	delete[]result;
	return 0;
}

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

double sqr( double x )
{
	return x * x;
}

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

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

		double a = x1 - x2, b = y1 - y2, c = -( sqr( x1 ) + sqr( y1 ) ) + ( sqr( x2 ) + sqr( y2 ) ),
			   d = x2 - x3, e = y2 - y3, f = -( sqr( x2 ) + sqr( y2 ) ) + ( sqr( x3 ) + sqr( y3 ) );

		double l = ( c * e - b * f ) / ( e * a - b * d ), m = ( c * d - a * f ) / ( b * d - a * e );
		double n = -( sqr( x1 ) + sqr( y1 ) + l * x1 + m * y1 );

		std::cout << std::fixed << std::setprecision( 3 );
		std::cout << -l / 2.0 << " " << -m / 2.0 << " " << sqrt( sqr( l ) + sqr( m ) - 4 * n ) / 2.0 << std::endl;
	}

	return 0;
}

C++: #include<bits/stdc++.h>
using namespace std;
typedef complex<double> point;
typedef pair<point, point> line;
double cross(point a, point b){
  return imag(conj(a) * b);
}


point cross_point(line a, line b){
  double d1 = cross(b.second - b.first,
                    b.first - a.first);
  double d2 = cross(b.second - b.first,
                    a.second - a.first);
  return a.first + (a.second - a.first) * (d1/d2);
}

int main(int argc, char *argv[]){
  int n;
  cin >> n;
  for (int i = 0; i < n; i++) {
    point x[3];
    for (int j = 0; j < 3; j++) {
      double real, imag;
      cin >> real >> imag;
      x[j] = point(real, imag);
    }
    point m1 = (x[0] - x[1]), m2 = (x[1] - x[2]);
    m1 = point(m1.real()/2, m1.imag()/2);
    m2 = point(m2.real()/2, m2.imag()/2);
    line n1 = line(m1*point(0, 1), m1*point(0, -1)),
      n2 = line(m2*point(0, 1), m2*point(0, -1));
    n1.first += m1 + x[1];
    n1.second += m1 + x[1];
    n2.first += m2 + x[2];
    n2.second += m2 + x[2];
    point center = cross_point(n1, n2);
    printf("%.3lf %.3lf %.3lf\n", center.real(), center.imag(),
           abs(center - x[0]));
  }
  return 0;
}