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<stdio.h>
#include<math.h>

using namespace std;

#define MAX 256

float LOSER(float x){
	if((int)(x*10000)%10 > 4)return x + 0.001;
	return x;
}

int main(void){
	int n,i = 0;
	float x1,y1,x2,y2,x3,y3;
	float px[MAX],py[MAX],r[MAX];
	
	cin >> n;
	while(i < n){
		cin >> x1 >> y1 >> x2 >> y2 >> x3 >> y3;
		px[i] = ((y1-y3)*(y1*y1-y2*y2+x1*x1-x2*x2)+(y1-y2)*(y1*y1-y3*y3+x1*x1-x3*x3))/(2*(y1-y3)*(x1-x2)+2*(y1-y2)*(x1-x3));
		py[i] = ((x1-x3)*(x1*x1-x2*x2+y1*y1-y2*y2)+(x1-x2)*(x1*x1-x3*x3+y1*y1-y3*y3))/(2*(x1-x3)*(y1-y2)+2*(x1-x2)*(y1-y3));
		r[i] = sqrt((px[i]-x1)*(px[i]-x1)+(py[i]-y1)*(py[i]-y1));
		//px[i]=LOSER(px[i]);
		//py[i]=LOSER(py[i]);
		//r[i]=LOSER(r[i]);
		i++;
		printf("%.3f %.3f %.3f",px[i],py[i],r[i]);
	}

	return 0;
}

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

#define N 10000
#define INF 200000000

int main()
{
    int n;
    vector<double> x(3), y(3), x2(3), y2(3);
    cin >> n;

    for(int p=0; p<n; p++)
    {
        cin >> x[0] >> y[0] >> x[1] >> y[1] >> x[2] >> y[2];
        for(int i=0; i<3; i++) { x2[i] = x[i]*x[i]; y2[i] = y[i]*y[i]; }

        double a, b, c, a2, b2, c2;
        a2 = abs((x[2]-x[1])*(x[2]-x[1]) + (y[2]-y[1])*(y[2]-y[1]));
        b2 = abs((x[0]-x[2])*(x[0]-x[2]) + (y[0]-y[2])*(y[0]-y[2]));
        c2 = abs((x[1]-x[0])*(x[1]-x[0]) + (y[1]-y[0])*(y[1]-y[0]));
        a = sqrt(a2); b = sqrt(b2); c = sqrt(c2);

        double s, S2;
        s = (a + b + c) / 2;
        S2 = s * (s-a) * (s-b) * (s-c);

        double cx, cy;
        cx = (a2*(b2+c2-a2)*x[0] + b2*(c2+a2-b2)*x[1] + c2*(a2+b2-c2)*x[2]) / (16 * S2);
        cy = (a2*(b2+c2-a2)*y[0] + b2*(c2+a2-b2)*y[1] + c2*(a2+b2-c2)*y[2]) / (16 * S2);

        cout << setprecision(3) << fixed <<
            cx << " " << cy << " " << sqrt(abs((cx-x[0])*(cx-x[0])+(cy-y[0])*(cy-y[0]))) << endl;
    }
}

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

//0010
int main(){
	int n;
	while(cin >> n){
		double x1,y1,x2,y2,x3,y3,x,y,r;

		while(n--){
			cin >> x1 >> y1 >> x2 >> y2 >> x3 >> y3;

			if(x1!=x2){
				x=(x1+x2)/2;
			}else if(x2!=x3){
				x=(x2+x3)/2;
			}else if(x3!=x1){
				x=(x3+x1)/2;
			}
			if(y1!=y2){
				y=(y1+y2)/2;
			}else if(y2!=y3){
				y=(y2+y3)/2;
			}else if(y3!=y1){
				y=(y3+y1)/2;
			}

			r=sqrt(pow(x-x1,2)+pow(y-y1,2));
			x+=0.0005;
			y+=0.0005;
			r+=0.0005;
			cout.setf(ios::fixed);
			cout.precision(3);
			cout << x << " " << y << " " << r << endl;
		}
	}

}

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

void gradcut(double *a,double *b,double x1,double y1,double x2,double y2);

int main() {
    double x[3],y[3],a[2],b[2],rx,ry,r;
    int n;
    std::cin >> n;
    for(int j=0;j<n;j++){
        int am=0,add=1;;
        for(int i=0;i<3;i++) std::cin >> x[i] >> y[i];
        for(int i=0;i<3;i++){
            if(i==2) add=-2;
            if(x[i]!=x[i+add]&&y[i]!=y[i+add]){
                gradcut(&a[am],&b[am],x[i],x[i+add],y[i],y[i+add]);
                am++;
                if(am>2) break;
            }else if(x[i]==x[i+add]){
                a[am]=0;
                b[am]=(y[i]+y[i+add])/2;
                am++;
                if(am>2) break;
            }
        }


        rx = (b[1]-b[0])/(a[0]-a[1]);
        ry = a[0]*rx+b[0];
        r=sqrt((x[0]-rx)*(x[0]-rx)+(y[0]-ry)*(y[0]-ry));
        printf("%.3f %.3f %.3f\n",rx,ry,r);
    }
    return 0;
}

void gradcut(double *a,double *b,double x1,double x2,double y1,double y2){

    *a=-(x2-x1)/(y2-y1);
    *b=(y1+y2)/2-*a*(x1+x2)/2;
}

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

double a,b,c,d,e,f,x,y,r;
int n;

double ifof(double a){
	int n = a*10000;
	if(n%10 >= 5)
		n++;
	return n/10000.0;
}

double solvex(){
	double k,l;
	k = (c*c)-(a*a)+(d*d)-(b*b)-(2*y*(d-b));
	l = 2*(c-a);
	return k/l;
}

double solvey(){
	double k,l;
	k = ((e-a)*((c*c)-(a*a)+(d*d)-(b*b)))-((c-a)*((e*e)-(a*a)+(f*f)-(b*b)));
	l = 2*(((d-b)*(e-a))-((f-b)*(c-a)));
	return k/l;
}

int main(){
	std::cin >> n;
	for(int i=0; i<n; i++){
		std::cin >> a >> b >> c >> d >> e >> f;
		y = solvey();
		x = solvex();
		r = std::sqrt(((x-a)*(x-a)) + ((y-b)*(y-b)));
		std::printf("%.3f %.3f %.3f\n",ifof(x),ifof(y),ifof(r));
	}
	return 0;
}