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 <cstdio>
#include <complex>
#include <vector>
#include <cmath>

using namespace std;

#define REP(i, n) for(int i = 0;i < n;i++)
#define REPR(i, n) for(int i = n;i >= 0;i--)
#define FOR(i, m, n) for(int i = m;i < n;i++)

typedef complex<double> P;
typedef vector<P> VP;
const double EPF = 1e-9;

#define X real()
#define Y imag()
#define EQ(x,y) (abs(x-y) < EPF)

double dot(P a, P b) {
  return (conj(a)*b).X;
}
double cross(P a, P b) {
  return (conj(a)*b).Y;
}
double distPP(P a, P b) {
  return sqrt(dot(a-b,a-b));
}
P crosspoint(P a, P b, P c, P d) {//ac & bd
  double d1 = cross(d-b,b-a);
  double d2 = cross(d-b,c-a);
  if(EQ(d1,0) & EQ(d2,0)) return a;
  if(EQ(d2,0)) return a;
  return a + (c-a)*d1/d2;
}
P normal_vector(P a) {
  P b(-a.Y, a.X);
  return b;
}

int main() {
  int n;
  scanf("%d", &n);
  REP(j, n) {
    VP a;
    REP(i, 3) {
      double x,y;
      scanf("%lf %lf", &x, &y);
      a.push_back(P(x,y));
    }
    P M = (a[0]+a[1])/(P)2;
    P N = (a[1]+a[2])/(P)2;
    P M_v = normal_vector(a[0]-a[1]);
    P N_v = normal_vector(a[1]-a[2]);

    P o = crosspoint(M, N, M+M_v, N+N_v);
    
    printf("%.3lf %.3lf %.3lf\n", o.X, o.Y, distPP(o,a[0]));
    a.clear();
  }
  return 0;
}

C++: #include <iostream>
#include <cstdio>
#include <stdio.h>
#include <math.h>
using namespace std;
int main(){
	int n;
	cin>>n;
	for(int i=0;i<n;i++){
		double x1,y1,x2,y2,x3,y3,xp,yp,r;
		cin>>x1>>y1>>x2>>y2>>x3>>y3;
		xp=0;
		yp=0;
		double a=y2-y1,b=y3-y1,c=y2-y3,d=x2-x1,e=x3-x1;
		if(y1 != y2 && y1 != y3){
			xp=(c/2-e*(x1+x3)/2/b-d*(x2+x1)/2/a)/(-e/b+d/a);
			yp=-e/b*(xp-(x1+x3)/2)+(y1+y3)/2;
		}else if(y1==y2){
			xp=(x1+x2)/2;
			yp=-e/b*(xp-(x1+x3)/2)+(y1+y3)/2;
		}else if(y1==y3){
			xp=(x1+x3)/2;
			yp=-d/a*(xp-(x1+x2)/2)+(y1+y2)/2;
		}
		r = sqrt((x1-xp)*(x1-xp)+(y1-yp)*(y1-yp));
		xp*=1000;
		xp+=0.5;
		int xp2=xp;
		yp*=1000;
		yp+=0.5;
		int yp2=yp;
		printf("%.3lf %.3lf %.3lf\n",xp2/(double)1000,yp2/(double)1000,r);
	}
	return 0;
}

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

double ceil2(double dIn, int nLen) {
	double dOut;

	dOut = dIn * pow(10.0, nLen);
	dOut = (double)(int)(dOut + 0.9);

	return dOut * pow(10.0, -nLen);
}

int main(void) {

	double x1[20], x2[20], x3[20], y1[20], y2[20], y3[20];
	double distance_12[20],distance_23[20],distance_31[20];
	int n = 0,i=0;
	double cosA,sinA,r,p,q;

	do {
		scanf("%d",&n);
	} while (n > 20);
	

	do {
		scanf("%lf%lf%lf%lf%lf%lf",&x1[i],&y1[i],&x2[i],&y2[i],&x3[i],&y3[i]);
		if((-100 <= (x1[i], x2[i], x3[i], y1[i], y2[i], y3[i])&&(100 >= (x1[i], x2[i], x3[i], y1[i], y2[i], y3[i]))))
		i++;
	} while (i < n);
	
	for (i = 0; i < n; i++) {
		distance_12[i] = sqrt(pow(x1[i] - x2[i], 2) + pow(y1[i] - y2[i], 2));
		distance_23[i] = sqrt(pow(x2[i] - x3[i], 2) + pow(y2[i] - y3[i], 2));
		distance_31[i] = sqrt(pow(x3[i] - x1[i], 2) + pow(y3[i] - y1[i], 2));
		}

	for (i = 0; i < n; i++) {
		p = ((y1[i] - y3[i])*(pow(y1[i],2) - pow(y2[i],2) + pow(x1[i],2) - pow(x2[i],2)) - (y1[i] - y2[i])*(pow(y1[i],2) - pow(y3[i],2) + pow(x1[i],2) - pow(x3[i],2))) / (2*(y1[i] - y3[i])*(x1[i] - x2[i]) - 2*(y1[i] - y2[i])*(x1[i] - x3[i]));
		q = ((x1[i] - x3[i])*(pow(x1[i],2) - pow(x2[i],2) + pow(y1[i],2) - pow(y2[i],2)) - (x1[i] - x2[i])*(pow(x1[i], 2) - pow(x3[i], 2) + pow(y1[i], 2) - pow(y3[i], 2))) / (2 * (x1[i] - x3[i])*(y1[i] - y2[i]) - 2 * (x1[i] - x2[i])*(y1[i] - y3[i]));
		cosA = (pow(distance_23[i], 2) + pow(distance_31[i], 2) - pow(distance_12[i], 2))/(2*distance_23[i]*distance_31[i]);
		sinA = sqrt(1 - pow(cosA, 2));
		r = distance_12[i] / (sinA * 2);
		printf("%.3lf %.3lf %.3lf\n",ceil2(p,4),ceil2(q,4),ceil2(r,4));
	}
	return 0;
}

C++: #include<bits/stdc++.h>
using namespace std;

int main(){

  double x1,y1,x2,y2,x3,y3;
  double px,py;
  int n;

  cin >> n;

  for(int i=0; i<n; i++){
    cin >> x1>>y1>>x2>>y2>>x3>>y3;
    px = ( (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 = ( (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));
    cout << px <<" "<< py <<" "<< sqrt((px-x1)*(px-x1)+(py-y1)*(py-y1)) << endl;

  }


  return 0;
}