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 argc,char* argv[]){
  double x1,y1,x2,y2,x3,y3;
  double x,y,r;
  double r12,r23,r31,angle1,angle2,angle3;
  int num,count;
  
  scanf("%d",&num);
  
  for(count = 0; num > count;count++){
    scanf("%lf %lf %lf %lf %lf %lf",&x1,&y1,&x2,&y2,&x3,&y3);
    
    r12 = sqrt((x1 -x2)*(x1 -x2) + (y1 -y2)*(y1 -y2));
    r23 = sqrt((x2 -x3)*(x2 -x3) + (y2 -y3)*(y2 -y3));
    r31 = sqrt((x3 -x1)*(x3 -x1) + (y3 -y1)*(y3 -y1));
    
    angle3 = acos( (r23*r23+r31*r31-r12*r12) / (2.0*r23*r31) );
    angle1 = acos( (r31*r31+r12*r12-r23*r23) / (2.0*r31*r12) );
    angle2 = acos( (r12*r12+r23*r23-r31*r31) / (2.0*r12*r23) );
    
    x = (sin(2.0*angle1)*x1 + sin(2.0*angle2)*x2 + sin(2.0*angle3)*x3)/(sin(2.0*angle1) + sin(2.0*angle2) + sin(2.0*angle3));
    y = (sin(2.0*angle1)*y1 + sin(2.0*angle2)*y2 + sin(2.0*angle3)*y3)/(sin(2.0*angle1) + sin(2.0*angle2) + sin(2.0*angle3));
    
    r = r23/ sin(angle1) / 2.0;
    
    printf("%.3lf %.3lf %.3lf\n",x,y,r);
  }
  
  return 0;
  
}

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

int main(){
  int n;
  double a,b,c,d,e,f,x,y,r;
  double x1,y1,x2,y2,x3,y3;

  std::cin >> n;

  for(int i=0;i<n;i++){
    std::cin >> x1>>y1>>x2>>y2>>x3>>y3;
    a = 2*(x1-x2);
    b = 2*(y1-y2);
    c = +(x1*x1-x2*x2)+(y1*y1-y2*y2);
    d = 2*(x2-x3);
    e = 2*(y2-y3);
    f = +(x2*x2-x3*x3)+(y2*y2-y3*y3);

    x = (double)(c*e-b*f)/(a*e-b*d);
    y = (double)(a*f-c*d)/(a*e-b*d);

    if(x == 0){x = 0;}
    if(y == 0){y = 0;}

    r = sqrt((x-x1)*(x-x1)+(y-y1)*(y-y1));

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

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

int n;
double x[3],y[3];
struct data{
	double a,b,c;
	data(double aa,double bb,double cc){
		a=aa;
		b=bb;
		c=cc;
	}
};

struct data2{
	double x,y,r;
	data2(){

	}
	data2(double xx,double yy,double rr){
		x=xx;
		y=yy;
		r=rr;
	}
};

data make_line(int i,int j){
	if(x[i]==x[j]){
		return data(0.0,(y[i]+y[j])/2.0,1);
	}
	if(y[i]==y[j]){
		return data((x[i]+x[j])/2,0,0); 
	}
	double aa=(y[i]-y[j])/(x[i]-x[j]);
	aa=-1.0/aa;
	double bb=(y[i]+y[j])/2.0-(x[j]+x[i])/2.0*aa;
	return data(aa,bb,1);
}

data2 cross(data y1,data y2){
	data2 d;
	if(y1.c==0){
		d.x=y1.a;
		d.y=y2.a*d.x+y2.b;
	}
	if(y2.c==0){
		d.x=y2.a;
		d.y=y1.a*d.x+y1.b;
	}
	if(y1.c==1 && y2.c==1){
		d.x=-(y1.b-y2.b)/(y1.a-y2.a);
		d.y=y1.a*d.x+y1.b;
	}
	d.r=sqrt(pow(d.x-x[0],2)+pow(d.y-y[0],2));
	return d; 
}

int main(void){
	scanf("%d",&n);
	for(int i=0;i<n;i++){
		for(int j=0;j<3;j++){
			scanf("%lf %lf",&x[j],&y[j]);
		}
		data y1=make_line(0,1);
		//printf("%.3f %.3f\n",y1.a,y1.b);
		data y2=make_line(0,2);
		//printf("%.3f %.3f\n",y2.a,y2.b);
		data2 y3=cross(y1,y2);
		printf("%.3f %.3f %.3f\n",y3.x,y3.y,y3.r);
	}
	return 0;
}

C++: #include <iostream>
#include <cstdio>
#include <cmath>
#define PI 3.141592653589793
using namespace std;
int main(){
	int n;
	cin>>n;
	for(int i=0;i<n;i++){
		double x,x2,x3,y,y2,y3,b,c,px,py,z;
		cin>>x>>x2>>x3>>y>>y2>>y3;
		b=sqrt(pow(x3-x2,2)+pow(y3-y2,2));
		c=sqrt(pow(x-x3,2)+pow(y-y3,2));
		z=asin(b/c);
		px=((y3-y)*(x2*x2-x*x+y2*y2-y*y)+(y-y2)*(x3*x3-x*x+y3*y3-y*y))/(2*(x2-x)*(y3-y)-(y2-y)*(x3-x));
		py=((x-x3)*(x2*x2-x*x+y2*y2-y*y)+(x2-x)*(x3*x3-x*x+y3*y3-y*y))/(2*(x2-x)*(y3-y)-(y2-y)*(x3-x));
		printf("%.3lf %.3lf %.3lf\n",px/2,py/2,(b/sin(z))/2);
	}
	return 0;
}

C++: #include <iostream>
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 a1=2*(x2-x1);
		double b1=2*(y2-y1);
		double c1=x1*x1-x2*x2+y1*y1-y2*y2;
		double a2=2*(x3-x1);
		double b2=2*(y3-y1);
		double c2=x1*x1-x3*x3+y1*y1-y3*y3;
		double x=(b1*c2-b2*c1)/(a1*b2-a2*b1);
		double y=(c1*a2-c2*a1)/(a1*b2-a2*b1);
		//	http://www.h6.dion.ne.jp/~jpe02_tn/ki-5.html

		double r = sqrt((x1-x)*(x1-x)+(y1-y)*(y1-y));

		printf( "%.3f %.3f %.3f\n", x, y, r );
	}
	return 0;

}