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>
#define P(x) pow(double(x),2)



void c_xpypr(){


}


int main(){


	int i,j,k;
	int n;
	double x[3],y[3];
	double xp,yp,r;
	double a1,a2,b1,b2,c1,c2;
	
	while((scanf("%d",&n))!=EOF){
		for(i=0;i<3;i++){
			scanf("%lf",&x[i]);
			scanf("%lf",&y[i]);
		}
		a1=2*(x[1]-x[0]);
		a2=2*(x[2]-x[1]);
		b1=2*(y[1]-y[0]);
		b2=2*(y[2]-y[1]);
		c1=(P(x[0])-P(x[1])+P(y[0])-P(y[1]));
		c2=(P(x[1])-P(x[2])+P(y[1])-P(y[2]));
	
		xp=(b1*c2-b2*c1)/(a1*b2-a2*b1);
		yp=(c1*a2-c2*a1)/(a1*b2-a2*b1);
		r=(double)(sqrt((long double)(((xp-x[0])*(xp-x[0]))+((yp-y[0])*(yp-y[0])))));	


		printf("%.3f %.3f %.3f\n",xp,yp,r);

	}



}

C++: #include<iostream>
#include<cmath>
#include<iomanip>
#include<array>

//#define P(p) pow 

using namespace std;

int main(){
	int N;
	cin>>N;
	for(int i=0;i<N;i++){
		array<pair<double,double>,3>p;
		cin>>p[0].first>>p[0].second>>p[1].first>>p[1].second>>p[2].first>>p[2].second;

		pair<long double, long double >o(
			 ((p[2].second - p[1].second) * (pow(p[1].first, 2.0) - pow(p[0].first, 2.0) + pow(p[1].second, 2.0) - pow(p[0].second, 2.0)) - (p[1].second - p[0].second) * (pow(p[2].first, 2.0) - pow(p[1].first, 2.0) + pow(p[2].second, 2.0) - pow(p[1].second, 2.0))) / (2.0 * ((p[1].first - p[0].first) * (p[2].second - p[1].second) - (p[1].second - p[0].second) * (p[2].first - p[1].first))),
                (- (p[2].first - p[1].first) * (pow(p[1].first, 2.0) - pow(p[0].first, 2.0) + pow(p[1].second, 2.0) - pow(p[0].second, 2.0)) + (p[1].first - p[0].first) * (pow(p[2].first, 2.0) - pow(p[1].first, 2.0) + pow(p[2].second, 2.0) - pow(p[1].second, 2.0))) / (2.0 * ((p[1].first - p[0].first) * (p[2].second - p[1].second) - (p[1].second - p[0].second) * (p[2].first - p[1].first)))
				);

		long double r=sqrt(pow(p[0].first - o.first, 2) + pow(p[0].second - o.second, 2));

		cout<<fixed<<setprecision(3)<<o.first<<" "<<o.second<<" "<<r<<endl;
	}
	return 0;
	
}

C++: #include <iostream>
#include <vector>
#include <fstream>
#include <algorithm>
#include <iomanip>
#include <map>
#include <queue>
#include <stack>
#include <set>
#include <ctime>
#include <iterator>
#include <sstream>
#include <cstdio>
#include <cstdlib>
#include <cmath>
using namespace std;

int main()
{
    int nb_cas;
    cin>>nb_cas;
    while(nb_cas--)
    {
        double x1,y1,x2,y2,x3,y3;
        cin>>x1>>y1>>x2>>y2>>x3>>y3;
        double a1=(x2-x1)*2;
        double b1=(y2-y1)*2;
        double c1=x1*x1-x2*x2+y1*y1-y2*y2;
        double a2=(x3-x1)*2;
        double b2=(y3-y1)*2;
        double c2=x1*x1-x3*x3+y1*y1-y3*y3;
        double xc=(b1*c2-b2*c1)/(a1*b2-a2*b1);
        double yc=(c1*a2-c2*a1)/(a1*b2-a2*b1);
        double r=sqrt((x1-xc)*(x1-xc)+(y1-yc)*(y1-yc));
        cout<<fixed<<setprecision(3)<<xc<<" "<<yc<<" "<<r<<endl;
    }
}

C++: /*
A1＝2(X2?X1)
B1＝2(Y2?Y1)
C1＝X12?X22＋Y12?Y22
A2＝2(X3?X1)
B2＝2(Y3?Y1)
C2＝X12?X32＋Y12?Y32

X＝(B1C2?B2C1)/(A1B2?A2B1)
Y＝(C1A2?C2A1)/(A1B2?A2B1)
*/
#include <fstream>
#include <iostream>
#include <math.h>
#include <vector>
#include <queue>
#include <utility>
#include <algorithm>
using namespace std;

int main() {
  // ifstream cin("../test.txt");
  int n;
  cin >> n;
  while (n--) {
    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 px = (b1 * c2 - b2 * c1) / (a1 * b2 - a2 * b1);
    double py = (c1 * a2 - c2 * a1) / (a1 * b2 - a2 * b1);

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

    printf("%.3f %.3f %.3f\n", px, py, r);
  }
}