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 <stdio.h>
#include <math.h>
 
int main()
{
    int i, n;
    double x1, x2, x3, y1, y2, y3;
    double a, b, c, d, e, f;
    double X1, Y1, r;
     
    scanf("%d", &n);
    for (i = 0; i < n; i++){
        scanf("%lf %lf %lf %lf %lf %lf",&x1, &y1, &x2, &y2, &x3, &y3);
        a = 2 * (x2 - x1);
        b = 2 * (y2 - y1);
        c = x1*x1 - x2*x2 + y1*y1 - y2*y2;
        d = 2 * (x3 - x1);
        e = 2 * (y3 - y1);
        f = x1*x1 - x3*x3 + y1*y1 - y3*y3;
         
        X1 = (b*f - e*c) / (a*e - d*b);
        Y1 = (c*d - f*a) / (a*e - d*b);
        r  = sqrt((X1-x1)*(X1-x1) + (Y1-y1)*(Y1-y1));
         
        X1 *= 1000;
        Y1 *= 1000;
        r  *= 1000;
         
        X1 = (int)(X1 > 0.0 ? X1+0.5 : X1-0.5);
        Y1 = (int)(Y1 > 0.0 ? Y1+0.5 : Y1-0.5);
        r  = (int)(r  > 0.0 ? r +0.5 : r -0.5);
         
        X1 = (double)X1/1000;
        Y1 = (double)Y1/1000;
        r  = (double)r /1000;
         
        printf("%.3f %.3f %.3f\n", X1, Y1, r);
         
         
    }
     
    return 0;
}

C++: #include<iostream>
#include<math.h>
#include<stdio.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 <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;
}