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 <stdio.h>

using namespace std;

struct point{
     double x, y;
};

void renritu(point p1, point p2, double *a, double *b, double *c){
    *a=2*(p2.x-p1.x);
    *b=2*(p2.y-p1.y);
    *c=p1.x*p1.x+p1.y*p1.y-(p2.x*p2.x+p2.y*p2.y);
}

int main(void){
    int i,n;
    point p1,p2,p3;
    cin >> n;
    for(i=0;i<n;i++){
        double a1,b1,c1,a2,b2,c2,r;
        cin >> p1.x >> p1.y >> p2.x >> p2.y >> p3.x >> p3.y;
        renritu(p1,p2,&a1,&b1,&c1);
        renritu(p1,p3,&a2,&b2,&c2);
        p3.x=-(b2*c1-b1*c2)/(a1*b2-a2*b1);
        p3.y=-(a1*c2-a2*c1)/(a1*b2-a2*b1);
        r=sqrt((p3.x-p1.x)*(p3.x-p1.x)+(p3.y-p1.y)*(p3.y-p1.y));
        printf("%.3lf %.3lf %.3lf\n",round(p3.x*1000)/1000,round(p3.y*1000)/1000, round(r*1000)/1000);
    }
    return 0;
}

C++: #include<complex>
#include<cstdio>
#include<cmath>
using namespace std;
typedef complex<double> P;
double F(double a,double b,double c){
	return acos((b*b+c*c-a*a)/(2*b*c));
}
int main(){
	int n;
	double d,e,f,g,h,i;
	for(scanf("%d",&n);n--;){
		scanf("%lf%lf%lf%lf%lf%lf",&d,&g,&e,&h,&f,&i);
		P a(d,g),b(e,h),c(f,i);
		double A=abs(b-c),B=abs(c-a),C=abs(a-b),
		s=sin(2*F(A,B,C)),t=sin(2*F(B,C,A)),u=sin(2*F(C,A,B)),v=s+t+u;
		printf("%.3f %.3f %.3f\n",(d*s+e*t+f*u)/v,(g*s+h*t+i*u)/v,A/sin(F(A,B,C))/2.);
	}
}

C++: #include <iostream>
#include<string>
#include<cmath>
#include<algorithm>
#include<cctype>
#include<queue>
#include<stack>
#include<stdio.h>
#include<vector>
#include<set>
#include<map>
#include<iomanip>
#define rep(i,n) for(int i=0;i<n;i++)
typedef int long long ll;
 
using namespace std;
int main(){
    int n;
    cin>>n;
    for(int i=0;i<n;i++){
    double a,b,c,d,e,f;
    cin>>a>>b>>c>>d>>e>>f;
    double x,y;
    y=((e-a)*(a*a+b*b-c*c-d*d)-(c-a)*(a*a+b*b-e*e-f*f))/(2*(e-a)*(b-d)-2*(c-a)*(b-f));
    if(c-a!=0){
         x=(2*(b-d)*y-a*a-b*b+c*c+d*d)/(2*(c-a));
    }else{
        x=(2*(b-f)*y-a*a-b*b+e*e+f*f)/(2*(e-a));
    }
    double r=sqrt(pow(x-a,2)+pow(y-b,2));
    printf("%.3f %.3f %.3f\n",x,y,r);
    }
     
     
    return 0;
}

C++: #include<iostream>
#include<cmath>
#include<algorithm>
#include<iomanip>
using namespace std;
class Point {
public:
	double x, y;
};
double distance(Point x, Point y) {
	return pow(pow(fabs(x.x - y.x), 2) + pow(fabs(x.y - y.y), 2), 0.5);
}
int main() {
	cout << setprecision(4);
	int n;
	cin >> n;
	for (int i = 0; i < n; i++) {
		Point p[3], s;
		for (int i = 0; i < 3; i++) {
			cin >> p[i].x >> p[i].y;
		}
		double a, b, c, d, e, f;
		a = (-2)*p[0].x + 2 * p[1].x;
		b = (-2)*p[0].y + 2 * p[1].y;
		c = (-2)*p[0].x + 2 * p[2].x;
		d = (-2)*p[0].y + 2 * p[2].y;
		e = pow(p[0].x, 2) + pow(p[0].y, 2) - pow(p[1].x, 2) - pow(p[1].y, 2);
		f = pow(p[0].x, 2) + pow(p[0].y, 2) - pow(p[2].x, 2) - pow(p[2].y, 2);
		s.x = (b*f - d*e) / (a*d - b*c);
		s.y = (a*f - c*e) / (b*c - a*d);
		double k = distance(p[0], s);
		s.x = round(s.x * 1000) / 1000;
		s.y = round(s.y * 1000) / 1000;
		k = round(k * 1000) / 1000;
		cout << s.x << " " << s.y << " " << k << endl;
	}
	return 0;
}

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

using namespace std;

typedef complex<double> Point;

bool eqv(double d1, double d2) {
    return abs(d1-d2) < 1e-10;
}

double r_(double x) {
    if(abs(x) < 0.001) return 0;
    return x;
}

int main() {
    int N;

    cin >> N;
    while(N--) {
        double x1, x2, x3, y1, y2, y3;
        cin >> x1 >> y1 >> x2 >> y2 >> x3 >> y3;
        Point p1(x1, y1), p2(x2, y2), p3(x3, y3);

        //³·è
        double R = abs(abs(p3-p2) / sin(arg(p2-p1) - arg(p3-p1))) / 2;

        Point vb = p3-p2;
        double len = sqrt(R*R - norm(vb)/4.0);
        Point vbh = vb * Point(0, 1);
        Point center = p2 + vb/2.0 + vbh*len/abs(vbh);
        if(eqv(abs(center-p1), R) && eqv(abs(center-p2), R) && eqv(abs(center-p3), R)) {}
        else center = p2 + vb/2.0 - vbh*len/abs(vbh);
        printf("%.3f %.3f %.3f\n", center.real(), center.imag(), R);
    }
    return 0;
}