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 _USE_MATH_DEFINES

#include <iostream>
#include <string>
#include <sstream>
#include <iomanip>
#include <cmath>
#include <algorithm>
#include <utility>
#include <vector>
#include <numeric>

using namespace std;

double distance(double x0, double y0, double x1, double y1)
{
	double x = x1 - x0;
	double y = y1 - y0;

	return sqrt(x * x + y * y);
}

int main()
{
	int n;
	for (cin >> n; n--;)
	{
		vector<double> x(3);
		vector<double> y(3);

		for (int i = 0; i < 3; i++)
		{
			cin >> x.at(i) >> y.at(i);
		}

		double a = distance(x.at(1), y.at(1), x.at(2), y.at(2));
		double b = distance(x.at(2), y.at(2), x.at(0), y.at(0));
		double c = distance(x.at(0), y.at(0), x.at(1), y.at(1));

		double cosA = (b * b + c * c - a * a) / (2 * b * c);
		double sinA = sqrt(1 - cosA * cosA);
		double r = a / (2 * sinA);

		double px = r * sinA;
		double py = r * cosA;

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

C++: #include<cstdio>
#include<cmath>
using namespace std;
int main(){
    int a;
    scanf("%d",&a);
    for(;;a--){
        double a1,a2,b1,b2,c1,c2,x1,y1,x2,y2,x3,y3;
        double x,y,r;
        scanf("%lf%lf%lf%lf%lf%lf",&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("%.3lf %.3lf %.3lf\n",x,y,r);
    }
    return 0;
}

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

#define rep(i,n) for(int i=0; i<n; i++)
int main(){
	double x1, x2, x3, y1, y2, y3;
	int n;
	cin >> n;
	rep(i, n){
		cin >> x1 >> y1 >> x2 >> y2 >> x3 >> y3;
		double a = sqrt(pow(x2-x3,2)+pow(y2-y3,2));
		double b = sqrt(pow(x3-x1,2)+pow(y3-y1,2));
		double c = sqrt(pow(x1-x2,2)+pow(y1-y2,2));
		double A = a*a;
		double B = b*b;
		double C = c*c;
		
		cout << (A*(B+C-A)*x1+B*(C+A-B)*x2+C*(A+B-C)*x3)/(A*(B+C-A)+B*(C+A-B)+C*(A+B-C)) << " ";
		cout << (A*(B+C-A)*y1+B*(C+A-B)*y2+C*(A+B-C)*y3)/(A*(B+C-A)+B*(C+A-B)+C*(A+B-C)) << " ";
		cout << a*b*c/sqrt((a+b+c)*(-a+b+c)*(a-b+c)*(a+b-c)) << endl;
	}
	return 0;
}