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 <bits/stdc++.h>

#define FOR(i,a,b) for(int i=a;i<b;i++)
#define REP(i,b) FOR(i,0,b)
#define MP make_pair

using namespace std;

inline double Square(double x){
	return x*x;
}

struct Pos{
	double x,y;
};

pair<Pos,double> ComputeCircle(Pos p,Pos q,Pos r){
	double a=-2.0*(p.x-q.x);
	double b=-2.0*(p.y-q.y);
	double c=Square(p.x)+Square(p.y)-Square(q.x)-Square(q.y);
	double d=-2.0*(p.x-r.x);
	double e=-2.0*(p.y-r.y);
	double f=Square(p.x)+Square(p.y)-Square(r.x)-Square(r.y);
	double k=1.0/(b*d-a*e);
	double x=(c*e-f*b)*k;
	double y=-(c*d-f*a)*k;
	double rad=sqrt(Square(p.x-x)+Square(p.y-y));
	return MP(Pos{x,y},rad);
}

int main(){
	int n;
	scanf("%d",&n);
	while(n--){
		Pos a,b,c;
		scanf("%lf%lf%lf%lf%lf%lf",&a.x,&a.y,&b.x,&b.y,&c.x,&c.y);
		auto p=ComputeCircle(a,b,c);
		printf("%.3f %.3f %.3f\n",p.first.x,p.first.y,p.second);
	}
}

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

using namespace std;

int main()
{
	int n;
	double x1, y1, x2, y2, x3, y3;
	double xp, yp, r;
	double a1, b1, c1, a2, b2 ,c2;
	cin>>n;
	for(int i=0;i<n;++i)
	{
		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;
		xp=(b1*c2-b2*c1)/(a1*b2-a2*b1);
		yp=(c1*a2-c2*a1)/(a1*b2-a2*b1);
		r=fabs(sqrt((x1+xp)*(x1+xp)+(y1+yp)*(y1+yp)));
		printf("%.3lf %.3lf %.3lf\n", xp, yp, r);
	}
}

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

int main()
{
	int n;
	cin >> n;
	for (int i = 0; i < n; i++){
		double x1, y1, x2, y2, x3, y3;
		cin >> x1 >> y1 >> x2 >> y2 >> x3 >> y3;
		double c1 = (x1 + x2) / 2;
		double c2 = (x1 + x3) / 2;
		double d1 = (y1 + y2) / 2;
		double d2 = (y1 + y3) / 2;
		double k1, k2, px, py, r;
		if (x1 != x2 && x1 != x3){
			k1 = (y2 - y1) / (x2 - x1);
			k2 = (y3 - y1) / (x3 - x1);
			py = (c2 - c1 + k2 * d2 - k1 * d1) / (k2 - k1);
			px = k1 * (d1 - py) + c1;
		}
		else{
			if (x1 == x2){
				py = d1;
				px = c2;
			}
			else if (x1 == x3){
				py = d2;
				px = c1;
			}
		}
		r = sqrt((px - x1)*(px - x1) + (py - y1)*(py - y1));

		cout << setprecision(3);
		cout << fixed;
		cout << px << " " << py << " " << r << endl;
	}
	return 0;
}

C++: #include <iostream>
#include <cmath>
#include <iomanip>
#define sqr(n) ((n) * (n))
using namespace std;

void equation(double a, double b, double c, double d, double e, double f, double *x, double *y)
{
  *x = (c * e - b * f) / (a * e - b * d);
  *y = (a * f - c * d) / (a * e - b * d);   
}

int main()
{
  int n;
  double x1, y1, x2, y2, x3, y3, x, y;
  cin >> n;
  for(int i = 0; i < n; i++){
    cin >> x1 >> y1 >> x2 >> y2 >> x3 >> y3;
    x = y = 0;
    equation((2 * (x2 - x1)), (2 * (y2 - y1)), (sqr(x2) + sqr(y2) - sqr(x1) - sqr(y1)), (2 * (x3 - x2)), (2 * (y3 - y2)), (sqr(x3) + sqr(y3) - sqr(x2) - sqr(y2)), &x, &y);
    cout << fixed << setprecision(3) << x + 0.0001 << ' ' <<  y + 0.0001 << ' ' << sqrt(sqr(x1 - x) + sqr(y1 - y)) + 0.0001 << endl;
  }
}