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 <iostream>
#include <algorithm>
#include <cstdio>
#include <cmath>
#include <string>
#include <cctype>
#include <stack>
#include <queue>
#include <vector>
#include <cstdlib>
#include <list>
#define _USE_MATH_DEFINES
#include <math.h>

using namespace std;

int main() {

	int n;
	double x1, x2, x3, y1, y2, y3;
	double X, Y, R;
	double a, b, c, d;

	cin >> n;

	for (int i = 0; i < n; i++) {
		cin >> x1 >> y1 >> x2 >> y2 >> x3 >> y3;

		a = x2 - x1;
		b = x3 - x1;
		c = y2 - y1;
		d = y3 - y1;
	
		X = 0.5*((a*a*d - b*b*c) + c*d*(d - c)) / (a*d - b*c);
		Y = 0.5*(a*b*(a - b) + (b*c*c - a*d*d)) / (b*c - a*d);
		R = sqrt((X - a)*(X - a) + (Y - a)*(Y - a));

		//?°???°????¬¬??????????????¨?????\
		if (X > 0)
			X = (int)(X * 1000 + 0.5);
		else X = (int)(X * 1000 - 0.5);

		if (Y>0)
			Y = (int)(Y * 1000 + 0.5);
		else Y = (int)(Y * 1000 - 0.5);

		if (R < 0)
			R = -R;
		R = (int)(R * 1000 + 0.5);

		
		printf("%.3lf %.3lf %.3lf\n", X/1000 , Y /1000, R /1000);
	}


	return 0;
}

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

int main(){
	int n;
	cin>>n;
	for(int i=0;i<n;n++){
		double ax,ay,bx,by,cx,cy,radab,radac,radc,r,bc;
		cin>>ax>>ay>>bx>>by>>cx>>cy;
		radab=atan2(by-ay,bx-ax);
		radac=atan2(cy-ay,cx-ax);
		radc=radac-radab;
		if(radc>M_PI_2)radc=M_PI-radc;
		bc=sqrt((cx-bx)*(cx-bx)+(cy-by)*(cy-by));
		r=bc/sin(radc)/2;
		printf("%.3f %.3f %.3f\n",ax+r*cos(radc+radab),ay+r*sin(radc+radab),r);
	}
	return 0;
}

C++: #include <iostream>
#include <vector>
#include <cstdio>
#include <cmath>
using namespace std;
#define x1 0
#define y1 1
#define x2 2
#define y2 3
#define x3 4
#define y3 5

int main()
{
	int n;
	double inp,a,b,c,d,e,f,x,y,r;
	vector<vector<double> > xy;

	cin>>n;
	xy.reserve(n);
	for(int i=0;i<n;i++)
	{
		for(int j=0;j<6;j++)
		{
			cin>>inp;
			xy[i].push_back(inp);
		}
		a=2*(xy[i][x2]-xy[i][x1]);
		b=2*(xy[i][y2]-xy[i][y1]);
		c=2*(xy[i][x3]-xy[i][x2]);
		d=2*(xy[i][y3]-xy[i][y2]);
		e=xy[i][y2]*xy[i][y2]-xy[i][y1]*xy[i][y1]+xy[i][x2]*xy[i][x2]-xy[i][x1]*xy[i][x1];
		f=xy[i][y3]*xy[i][y3]-xy[i][y2]*xy[i][y2]+xy[i][x3]*xy[i][x3]-xy[i][x2]*xy[i][x2];

		x=(d*e-b*f)/(a*d-b*c);
		y=(a*f-c*e)/(a*d-b*c);
		r=sqrt(pow(xy[i][x1]-x,2)+pow(xy[i][y1]-y,2));

		x+=0.0005;
		y+=0.0005;
		r+=0.0005;

		printf("%.3lf %.3lf %.3lf\n",x,y,r);
	}
}

C++: #include<iostream>
#include<stdio.h>
#include<math.h>
using namespace std;
int main()
{
    double x1,y1,x2,y2,x3,y3;
    int n;
    while(n--)
    {
        cin>>x1>>y1>>x2>>y2>>x3>>y3;
         double  d1 = x1*x1+y1*y1;
      double  d2 = x2*x2+y2*y2;
      double  d3 = x3*x3+y3*y3;
      double  u = 0.5/(x1*y2-x2*y1+x2*y3-x3*y2+x3*y1-x1*y3);
      double  xp = u*(d1*y2-d2*y1+d2*y3-d3*y2+d3*y1-d1*y3);
      double  yp = u*(x1*d2-x2*d1+x2*d3-x3*d2+x3*d1-x1*d3);
      double  r = sqrt((xp-x1)*(xp-x1)+(yp-y1)*(yp-y1));
      printf("%.3f %.3f %.3f\n",xp,yp,r);
    }



    return 0;
}

C++: #include<iostream>
#include<cmath>
using namespace std;
int main() {
  int n=0;
  double ax,ay,bx,by,cx,cy,S,R,a,b,c,x=0,y=0;
  cin>>n;
  for(int i=0; i<n; i++){
    cin>>ax>>ay>>bx>>by>>cx>>cy;
    S=((bx-ax)*(cy-ay)-(cx-ax)*(by-ay))/2;
    a=sqrt((ax-bx)*(ax-bx)+(ay-by)*(ay-by));
    b=sqrt((cx-bx)*(cx-bx)+(cy-by)*(cy-by));
    c=sqrt((ax-cx)*(ax-cx)+(ay-cy)*(ay-cy));
    R=a*b*c/(4*S);
    x=(a*a*(b*b+c*c-a*a)*ax+b*b*(c*c+a*a-b*b)*bx+c*c*(a*a+b*b-c*c)*cx)/(16*S*S);
    y=(a*a*(b*b+c*c-a*a)*ay+b*b*(c*c+a*a-b*b)*by+c*c*(a*a+b*b-c*c)*cy)/(16*S*S);
    cout<<x<<" "<<y<<" "<<R<<endl;
  }
}