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<cmath>
#include<cstdio>
using namespace std;
int main(){

  double x1,x2,x3,y1,y2,y3;
  int n;
  cin >> n;
  for(int i=0;i<n;i++){
    cin>>x1>>y1>>x2>>y2>>x3>>y3;
    double ax,ay,a,b,c,d,e,f,r;
    if(y2!=y1){
      a=-(x2-x1)/(y2-y1);
      b=-1;
      c=-a*(x1+x2)/2+(y1+y2)/2;
    }else{
      a=1;
      b=0;
      c=(x1+x2)/2;
    }
    if(y3!=y2){
      d=-(x3-x2)/(y3-y2);
      e=-1;
      f=-a*(x2+x3)/2+(y2+y3)/2;
    }else{
      d=1;
      e=0;
      f=(x2+x3)/2;
    }
    ax=(c*e-b*f)/(a*e-b*d);
    ay=(a*f-c*d)/(a*e-b*d);
    if(ax==0)
      ax=0;
    if(ay==0)
      ay=0;
    r=sqrt((x1-ax)*(x1-ax)+(y1-ay)*(y1-ay));
    if(ax*1000-(int)ax*1000>=0.5)
      ax+=0.001;
    if(ay*1000-(int)ay*1000>=0.5)
      ay+=0.001;
    printf("%.3f %.3f %.3f\n",ax,ay,r);
  }

}

  //y=a(x-a1)+b1
  //y=ax-a*a1+b1
  //ax-y=-a*a1+b1

C++: #include<iostream>
#include<cmath>
#include<cstdio>

using namespace std;

int main()
{
    int n;
    cin >> n;
    double x1,y1,x2,y2,x3,y3;
    while(n>0)
    {
        cin >> x1 >> y1 >>x2 >> y2 >> x3 >> y3;
        double s,v1x,v1y,v2x,v2y;
        v1x = y2-y1;
        v1y = x1-x2;

        v2x = y3-y1;
        v2y = x1-x3;
        double detA = v1x*v2y-v1y*v2x;
        double hx = (x2+x1)/2;
        double hy = (y2+y1)/2;
        s = (v2y*(x2-x1)/2 -v2x*(y2-y1)/2)/detA;
        double ox,oy;
        ox = hx + s*v1x;
        oy = hy + s*v1y;
        if(-0.0005<ox&&ox<0)ox = 0;
        if(-0.0005<oy&&oy<0)oy = 0;
        double r = sqrt((x1-ox)*(x1-ox)+(y1-oy)*(y1-oy));
        printf("%.3f %.3f %.3f\n",ox,oy,r);
        --n;
    }
    return 0;
}

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, e, f;

	cin >> n;

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

		a = -x2 + x3;
		b = -x1*x1 + x2*x2 - y1*y1 + y2*y2;
		c = x1 - x2;
		d = -x2*x2 + x3*x3 - y2*y2 + y3*y3;
		e = -c * 2 * (y2 - y3);
		f = a * 2 * (y1 - y2);

		Y = (a*b + c*d) / (e - f);
		X = (b + 2 * Y*(y1 - y2)) / (-2 * c);
		R = sqrt((X - x1)*(X - x1) + (Y - y1)*(Y - y1));

		//?°???°????¬¬??????????????¨?????\
		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("%.3f %.3f %.3f\n", X / 1000, Y / 1000, R / 1000);
	}

	return 0;
}

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

#define rep(i,n) for(int i=0; i<n; i++)
int main(){
	double x1, x2, x3, y1, y2, y3;
	int n;
	cin >> n;
	rep(i, n){
		cin >> x1 >> y1 >> x2 >> y2 >> x3 >> y3;
		double a = sqrt(pow(x2-x3,2)+pow(y2-y3,2));
		double b = sqrt(pow(x3-x1,2)+pow(y3-y1,2));
		double c = sqrt(pow(x1-x2,2)+pow(y1-y2,2));
		double A = a*a;
		double B = b*b;
		double C = c*c;
		
		double px= (A*(B+C-A)*x1+B*(C+A-B)*x2+C*(A+B-C)*x3)/(A*(B+C-A)+B*(C+A-B)+C*(A+B-C));
		double py= (A*(B+C-A)*y1+B*(C+A-B)*y2+C*(A+B-C)*y3)/(A*(B+C-A)+B*(C+A-B)+C*(A+B-C));
		double r= a*b*c/sqrt((a+b+c)*(-a+b+c)*(a-b+c)*(a+b-c));
		printf("%.3lf %.3lf %.3lf\n", px, py, r);
	}
	return 0;
}