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 <iomanip>
#include <cmath>
using namespace std;

inline sqr(double x){return x*x;}
inline double Roundoff(double x){
	if( x<0 ){
		x*=-1;
		x=(x-(x-int(x*1000)/1000))+(((x*1000)-int(x*1000))*10)>=4?0.001:0;
		x*=-1;
	}else{
		x=(x-(x-int(x*1000)/1000))+(((x*1000)-int(x*1000))*10)>=4?0.001:0;
	}
	return x;
}

void SolveSimultEq(double &x,double &y,double a,double b,double c,double d,double e,double f);
int main(){
	int datanum;
	double *x1,*y1,*x2,*y2,*x3,*y3;
	cin>>datanum;
	x1=new double[datanum];
	y1=new double[datanum];
	x2=new double[datanum];
	y2=new double[datanum];
	x3=new double[datanum];
	y3=new double[datanum];
	
	for( int i=0;i<datanum;i++ ){
		cin>>x1[i]>>y1[i]>>x2[i]>>y2[i]>>x3[i]>>y3[i];
	}
	for( int i=0;i<datanum;i++ ){
		double px,py,r;
		
		SolveSimultEq(px,py,2*(x1[i]-x2[i]),2*(y1[i]-y2[i]),sqr(x1[i])-sqr(x2[i])+sqr(y1[i])-sqr(y2[i]),
  			  	    2*(x2[i]-x3[i]),2*(y2[i]-y3[i]),sqr(x2[i])-sqr(x3[i])+sqr(y2[i])-sqr(y3[i]));
		r=sqrt(sqr(x1[i]-px)+sqr(y1[i]-py));
		cout<<fixed<<setprecision(3)<<px<<" "<<setprecision(3)<<py<<" "<<setprecision(3)<<r<<endl;

	}

	delete x1;
	delete y1;
	delete x2;
	delete y2;
	delete x3;
	delete y3;
	return 0;
}

void SolveSimultEq(double &x,double &y,double a,double b,double c,double d,double e,double f){
	double delta=a*e-b*d;
	
	x=(c*e-b*f)/delta;
	y=(a*f-c*d)/delta;
}

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

double sisya(double x)
{
	int a = static_cast<int>(x * 10000);
	x = static_cast<double>(static_cast<int>(x * 1000)) / 1000;
	if(a < 0 && a%10 <= -5)
		return x-0.001;
	else if(a%10 >= 5)
		return x+0.001;
	return x;
}

double dif(double x,double y,double xx, double yy)
{
	return sqrt((x-xx)*(x-xx)+(y-yy)*(y-yy));
}

int main()
{
	int n;
	double x1,x2,x3,y1,y2,y3;
	cin >> n;
	for(int i=0;i<n;i++){
		cin >> x1 >> y1 >> x2 >> y2 >> x3 >> y3;
		double px = max(x1,max(x2,x3)) - (max(x1,max(x2,x3)) - min(x1,min(x2,x3))) / 2;
		double py = max(y1,max(y2,y3)) - (max(y1,max(y2,y3)) - min(y1,min(y2,y3))) / 2;
		double r  = dif(x1,y1,px,py);
		cout << setprecision(3) << fixed << sisya(px) << " " << setprecision(3) << fixed << sisya(py) << " " << setprecision(3) << fixed << sisya(r) <<endl;
	}
	return 0;
}

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

using namespace std;

#define rep(i, n) for (int i = 0; i < int(n); ++i)

#define X real()
#define Y imag()

typedef long double D;
typedef complex<D> P;

D aTri(D a, D b, D c){
  D s = (a + b + c) / 2;
  return sqrt(max(s * (s - a) * (s - b) * (s - c), (D)0));
}

P circumscribedCircleCenter(P a, P b, P c) {
  D ax = a.X, ay = a.Y;
  D bx = b.X, by = b.Y;
  D cx = c.X, cy = c.Y;
  D d = 2 * (ax * (by - cy) + bx * (cy - ay) + cx * (ay - by));
  return P(((ay * ay + ax * ax) * (by - cy) + by * by + bx * bx * (cy - ay) +
	    (cy * cy + cx * cx) * (ay - by)) / d,
	   ((ay * ay + ax * ax) * (cx - bx) + by * by + bx * bx * (ax - cx) +
	    (cy * cy + cx * cx) * (bx - ax)) / d);
}

D circumscribedCircleRadius(D a, D b, D c) {return a * b * c / (4 * aTri(a, b, c));}

int main() {
  int n;
  cin >> n;
  rep (i, n) {
    P a, b, c;
    cin >> a.X >> a.Y >> b.X >> b.Y >> c.X >> c.Y;
    P p = circumscribedCircleCenter(a, b, c);
    D r = circumscribedCircleRadius(abs(a - b), abs(b - c), abs(c - a));
    printf("%.3Lf %.3Lf %.3Lf\n", p.X, p.Y, r);
  }
  return 0;
}

C++: #include<iostream>
#include<math.h>
#include <iomanip>
using namespace std;
int main() {
	int n;
	cin >> n;

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

		float px, py, r;
		float A1, B1, C1, A2, B2, C2;
		A1 = 2 * (x2 - y2);
		B1 = 2 * (y2 - y1);
		C1 = x1*x1 - x2*x2 + y1*y1 - y2*y2;
		A2 = 2 * (x3 - x1);
		B2 = 2 * (y3 - y1);
		C2 = x1*x1 - x3*x3 + y1*y1 - y3*y3;

		px = (B1*C2 - B2*C1) / (A1*B2 - A2*B1);
		py = (C1*A2 - C2*A1) / (A1*B2 - A2*B1);

		r = sqrt((x1 - px)*(x1 - px) + (y1 - py)*(y1 - py));

		px = round(px * 1000) / 1000;
		py = round(py * 1000) / 1000;
		r = round(r * 1000) / 1000;
		cout << fixed << setprecision(3) << px << " ";
		cout << fixed << setprecision(3) << py << " ";
		cout << fixed << setprecision(3) << r << endl;
	}
	return 0;

}