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>

#define SQ(x) ((x) * (x))

int main(void)
{
    int s;
    int i;
    double x1, x2, x3;
    double y1, y2, y3;
    double a, b, c, d, e, f;
    double l, m, n;
    
    scanf("%d", &s);
    for (i = 0; i < s; i++){
        scanf("%lf%lf%lf%lf%lf%lf", &x1, &y1, &x2, &y2, &x3, &y3);
        
        a = (x1 - x2);
        b = (y1 - y2);
        c = -1 * (SQ(x1) - SQ(x2) + SQ(y1) - SQ(y2));
        d = (x1 - x3);
        e = (y1 - y3);
        f = -1 * (SQ(x1) - SQ(x3) + SQ(y1) - SQ(y3));
        
        l = (c * e - b * f) / (e * a - b * d);
        m = (d * c - a * f) / (d * b - e * a);
        
        n = -1 * (SQ(x1) + SQ(y1) + l * x1 + m * y1);
        
        printf("%.3f %.3f %.3f\n", l / -2.0, m / -2.0, sqrt(SQ(l) + SQ(m) - 4 * n) / 2.0);
    }
    
    return (0);
}

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

int main(){

  double x[3], y[3], mx, my, lx, ly, dm, dl, cx, cy, r;
  
  for(int i=0; i<3; i++){
    cin >> x[i] >> y[i];
  }
  
  mx = (x1 + x2) / 2;
  my = (y1 + y2) / 2;
  dm = (y1 - y2) / (x1 - y2);
  lx = (x2 + x3) / 2;
  ly = (y2 + y3) / 2;
  dl = (y2 - y3) / (x2 - x3);
  cx = (my + dm * mx) - (ly + dl * lx);
  cy = (ly + dl * lx) * dm - (my + dm * mx) * dl;
  
  r = sqrt((x1 - cx) * (x1 - cx) + (y1 - cy) * (y1 - cy));

  cx = round(cx * 1000) / 1000;
  cy = round(cy * 1000) / 1000;
  r = round(r * 1000) / 1000;

  printf("%.3f %.3f %.3f\n", cx, cy, r);

  return 0;
}

C++: #include<iostream>
#include<cstdio>
#include<cmath>
using namespace std;
int n; double a, b, c, d, e, f;
int main() {
	cin >> n;
	for (int i = 0; i < n; i++) {
		cin >> a >> b >> c >> d >> e >> f; double C = sqrt((a - c)*(a - c) + (b - d)*(b - d));
		double B = sqrt((a - e)*(a - e) + (b - f)*(b - f)), A = sqrt((c - e)*(c - e) + (d - f)*(d - f));
		double A1 = 2 * (c - a), B1 = 2 * (d - b), A2 = 2 * (e - a), B2 = 2 * (f - b), C1 = a*a - c*c + b*b - d*d, C2 = a*a - e*e + b*b - f*f;
		double X = (B1*C2 - B2*C1) / (A1*B2 - A2*B1), Y = (C1*A2 - C2*A1) / (A1*B2 - A2*B1);
		double R = (A*B*C) / sqrt((A + B + C)*(-A + B + C)*(A - B + C)*(A + B - C));
		printf("%.3lf %.3lf %.3lf\n", X, Y, R);
	}
	return 0;
}

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

struct Zahyou
{
	float x, y;
};

int main()
{
	int n;
	Zahyou de[4];

	scanf("%d", &n);
	for (int i = 0; i < n; i++)
	{
		for (int j = 1; j < 4; j++)
		{
			scanf("%f %f", &de[j].x, &de[j].y);
		}
		de[0].x = ((de[1].y - de[3].y)*(pow(de[1].y, 2) - pow(de[2].y, 2) + pow(de[1].x, 2) - pow(de[2].x, 2)) - (de[1].y - de[2].y)*(pow(de[1].y, 2) - pow(de[3].y, 2) + pow(de[1].x, 2) - pow(de[3].x, 2))) / (2 * (de[1].y - de[3].y)*(de[1].x - de[2].x) - 2 * (de[1].y - de[2].y)*(de[1].x - de[3].x));
		de[0].y = ((de[1].x - de[3].x)*(pow(de[1].x, 2) - pow(de[2].x, 2) + pow(de[1].y, 2) - pow(de[2].y, 2)) - (de[1].x - de[2].y)*(pow(de[1].x, 2) - pow(de[3].x, 2) + pow(de[1].y, 2) - pow(de[3].y, 2))) / (2 * (de[1].x - de[3].x)*(de[1].y - de[2].y) - 2 * (de[1].x - de[2].x)*(de[1].y - de[3].y));
		
		printf("%.3f %.3f %.3f\n",de[0].x,de[0].y,sqrt(de[0].x+de[0].y));
	}
	return 0;
}

C++: #include <iostream>
#include <math.h>
#include <cstdio>
using namespace std;
int main()
{
    int n;
    double ax,ay,bx,by,cx,cy,x,y,r;
    double A1,B1,C1,A2,B2,C2;
    cin>>n;
    while(n--){
        cin>>ax>>ay>>bx>>by>>cx>>cy;
        A1=2*(bx-ax);
        B1=2*(by-ay);
        C1=ax*ax-bx*bx+ay*ay-by*by;
        A2=2*(cx-ax);
        B2=2*(cy-ay);
        C2=ax*ax-cx*cx+ay*ay-cy*cy;
        x=(B1*C2-B2*C1)/(A1*B2-A2*B1);
        y=(C1*A2-C2*A1)/(A1*B2-A2*B1);
        r=sqrt((ax-x)*(ax-x)+(ay-y)*(ay-y));
        printf("%.3f %.3f %.3f\n",x,y,r);
    }
    return 0;
}