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++: using System;

class main
{
    static void Main(string[] args)
    {
        string s = string.Empty;
        var n = int.Parse(Console.ReadLine());        
        while (n-- != 0)
        {
            s = Console.ReadLine();
            string[] s1 = s.Split(' ');
            double x1 = double.Parse(s1[0]);
            double x2 = double.Parse(s1[1]);
            double x3 = double.Parse(s1[2]);
            double y1 = double.Parse(s1[3]);
            double y2 = double.Parse(s1[4]);
            double y3 = double.Parse(s1[5]);
            double a = Math.Sqrt((x1 - x2) * (x1 - x2) + (y1 - y2) * (y1 - y2));
            double b = Math.Sqrt((x2 - x3) * (x2 - x3) + (y2 - y3) * (y2 - y3));
            double c = Math.Sqrt((x3 - x1) * (x3 - x1) + (y3 - y1) * (y3 - y1));
            double r = (a * b * c) / Math.Sqrt((a + b + c) * (-a + b + c) * (a - b + c) * (a + b - c));
            double x = (((x1 * x1 + y1 * y1) * (y2 - y3)) + ((x2 * x2 + y2 * y2) * (y3 - y1)) + ((x3 * x3 + y3 * y3) * (y1 - y2))) / ((x1 * (y2 - y3)) + (x2 * (y3 - y1)) + (x3 * (y1 - y2))) * 0.5;
            double y = (((x1 * x1 + y1 * y1) * (x2 - x3)) + ((x2 * x2 + y2 * y2) * (x3 - x1)) + ((x3 * x3 + y3 * y3) * (x1 - x2))) / ((y1 * (x2 - x3)) + (y2 * (x3 - x1)) + (y3 * (x1 - x2))) * 0.5;
            Console.WriteLine("{0:F3} {1:F3} {2:F3}", x, y, r);
        }
        Console.ReadKey();
    }
}

C++: #include<iostream>
#include<cstdio>
#include<cmath>
using namespace std;
int main()
{
	int n;cin>>n;
	double x1,x2,x3,y1,y2,y3,x12,x13,y12,y13,xx12,yy12,xx13,yy13,x,y,r;
	for(int i=0;i<n;i++)
	{
		cin>>x1>>y1>>x2>>y2>>x3>>y3;
		
		x12=x1-x2;
		x13=x1-x3;
		y12=y1-y2;
		y13=y1-y3;
		xx12=x1*x1-x2*x2;
		xx13=x1*x1-x3*x3;
		yy12=y1*y1-y2*y2;
		yy13=y1*y1-y3*y3;
		
		x=-0.5*(y12*(xx13+yy13)-y13*(xx12+yy12))/(x12*y13-x13*y12);
		y=-0.5*(x12*(xx13+yy13)-x13*(xx12+yy12))/(y12*x13-y13*x12);
		r=sqrt(x*x+y*y+x1*x1+y1*y1-2*x*x1-2*y*y1);
		
		printf("%.3lf %.3lf %.3lf\n",x,y,r);
		
	}
	return 0;
}

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

using namespace std;

int main(){
	int n;
	double x1,y1,x2,y2,x3,y3,px,py,r;
	cin>>n;
	while(n--){
		cin>>x1>>y1>>x2>>y2>>x3>>y3;
		px=-1.0/2*((x2*x2-x1*x1)*(y3-y1)-(x3*x3-x1*x1)*(y2-y1)+(y3-y1)*(y2-y1)*(y2-y3))/((x3-x1)*(y2-y1)-(x2-x1)*(y3-y1));
		if(y2-y1 != 0){
			py=-(x2-x1)/(y2-y1)*(px-(x1+x2)/2)+(y1+y2)/2;
		}else{
			py=-(x3-x1)/(y3-y1)*(px-(x1+x3)/2)+(y1+y3)/2;
		}
		r=sqrt((px-x1)*(px-x1)+(py-y1)*(py-y1));
		cout<<px<<' '<<py<<' '<<r<<endl;
	}
	return 0;
}