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 <cstdio>
#include <complex.h>
#include <vector>
#define EPS 1e-10
#define EQ(a, b) (abs((a) - (b)))
using namespace std;

typedef complex<double> P;
double cross(P a, P b) {
    return(a.real() * b.imag() - a.imag() * b.real());
}

int main(void) {
    int num; cin >> num;
    
    for(int r = 0; r < num; r++) {
        vector<P> vec;
        for(int c = 0; c < 3; c++) {
            double x, y; cin >> x >> y;
            vec.push_back(P(x, y));
        }
        //中点
        P mid1((vec[0] + vec[1]) / 2.0), mid2((vec[1] + vec[2]) / 2.0);
        //法線ベクトル
        cout << mid1  << " " << mid2 << endl;
        P cross1((vec[0] - vec[1]) * P(0, 1)), cross2((vec[1] - vec[2]) * P(0, 1));
        cout << cross1  << " " << cross2 << endl;
        //交点
        P ans(mid1 + cross1 * cross(cross2, (mid2 - mid1)) / cross(cross2, cross1));
        double half_r = abs(ans - vec[0]);
        printf("%.3f %.3f %.3f\n", ans.real(), ans.imag(), half_r);
    }
    return(0);
}

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-5;

#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);
  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]));
  
  return 0;
}

C++: #include<iostream>
#include <fstream>
#include <stdio.h>
#include <stdlib.h>
#define _USE_MATH_DEFINES
#include <math.h>
#include<string>
#include<vector>
#include<cmath>
#include<stack>
#include<queue>
#include<sstream>
#include<algorithm>
#include<map>
#include<complex>
using namespace std;


#define li			long long int
#define rep(i,to)	for(int i=0;i<((int)(to));i++)
#define repp(i,start,to)	for(int i=(int)(start);i<((int)(to));i++)
#define pb			push_back
#define sz(v)		((li)(v).size())
#define bgn(v)		((v).begin())
#define eend(v)		((v).end())
#define allof(v)	(v).begin(), (v).end()
#define dodp(v,n)		memset(v,(li)n,sizeof(v))
#define bit(n)		(1ll<<(li)(n))
#define mp(a,b)		make_pair(a,b)
#define rin	rep(i,n)
#define EPS 1e-10
#define ETOL 1e-8
#define MOD 1000000007
#define p2(a,b)		cout<<a<<"\t"<<b<<endl
#define p3(a,b,c)		cout<<a<<"\t"<<b<<"\t"<<c<<endl

double a[6];

void solve(){
	double x,y;
	double c[2];
	c[0]=(a[0]+a[2])/2.0;
	c[1]=(a[1]+a[3])/2.0;
	
	double l1[2], k1[2];
	k1[0]=-(a[3]-a[1]);
	k1[1]=(a[2]-a[0]);
	
	double d[2];
	d[0]=(a[4]+a[2])/2.0;
	d[1]=(a[5]+a[3])/2.0;
	
	double l2[2], k2[2];
	k2[0]=-(a[3]-a[5]);
	k2[1]=(a[2]-a[4]);
	
	if(k1[0]==0){
		x=c[0];
		l2[0]=k2[1]/k2[0];
		l2[1]=-l2[0]*d[0]+d[1];
		y=l2[0]*x+l2[1];
		
	}
	else if(k2[0]==0){
		x=d[0];
		l1[0]=k1[1]/k1[0];
		l1[1]=-l1[0]*c[0]+c[1];
		y=l1[0]*x+l1[1];
	}
	else{
		l1[0]=k1[1]/k1[0];
		l1[1]=-l1[0]*c[0]+c[1];
		
		l2[0]=k2[1]/k2[0];
		l2[1]=-l2[0]*d[0]+d[1];
		
		x=-(l2[1]-l1[1])/(l2[0]-l1[0]);
		y=l1[0]*x+l1[1];
	}
	double r=sqrt((x-a[0])*(x-a[0])+(y-a[1])*(y-a[1]));
	
	printf("%.3f %.3f %.3f\n",x,y,r);
}

int main(){
	li n;
	cin>>n;
	
	rin{
		rep(j,6)cin>>a[j];
		solve();
	}
	
	return 0;
}