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 <bits/stdc++.h>

using namespace std;

#define LOG(...) fprintf(stderr, __VA_ARGS__)
//#define LOG(...)
#define FOR(i, a, b) for(int i=(int)(a); i<(int)(b); ++i)
#define REP(i, n) for(int i=0; i<(int)(n); ++i)
#define ALL(a) (a).begin(), (a).end()
#define RALL(a) (a).rbegin(), (a).rend()
#define EXIST(s, e) ((s).find(e)!=(s).end())
#define SORT(c) sort(ALL(c))
#define RSORT(c) sort(RALL(c))
#define SQ(n) (n) * (n)

typedef long long ll;
typedef unsigned long long ull;
typedef vector<bool> vb;
typedef vector<int> vi;
typedef vector<ll> vll;
typedef vector<vb> vvb;
typedef vector<vi> vvi;
typedef vector<vll> vvll;
typedef pair<int, int> pii;
typedef pair<ll, ll> pll;

int main() {
  int n;
  double x1, y1, x2, y2, x3, y3;
  cin >> n;
  REP(i, n){
    cin >> x1 >> y1 >> x2 >> y2 >> x3 >> y3;
    double a = 2 * (x2 - x1);
    double b = 2 * (y2 - y1);
    double e = x2 * x2 + y2 * y2 - x1 * x1 - y1 * y1;
    double c = 2 * (x3 - x2);
    double d = 2 * (y3 - y2);
    double f = x3 * x3 + y3 * y3 - x2 * x2 - y2 * y2;

    double D = 1 / (a * d - b * c);
    double x = (d * e - b * f) * D;
    double y = (-c * e + a * f) * D;
    double r = sqrt(SQ(x1 - x) + SQ(x1 - y));
    printf("%.3f %.3f %.3f\n", x, y, r);
  }
}

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

void gradcut(double *a,double *b,double x1,double y1,double x2,double y2);

int main() {
    double x[3],y[3],a[2],b[2],rx,ry,r;
    int n;
    std::cin >> n;
    for(int j=0;j<n;j++){
        int am=0,add=1;;
        for(int i=0;i<3;i++) std::cin >> x[i] >> y[i];
        for(int i=0;i<3;i++){
            if(i==2) add=-2;
            if(x[i]!=x[i+add]&&y[i]!=y[i+add]){
                gradcut(&a[am],&b[am],x[i],x[i+add],y[i],y[i+add]);
                am++;
                if(am>2) break;
            }else if(x[i]==x[i+add]){
                a[am]=0;
                b[am]=(y[i]+y[i+add])/2;
                am++;
                if(am>2) break;
            }
        }


        rx = (b[1]-b[0])/(a[0]-a[1]);
        ry = a[0]*rx+b[0];
        r=sqrt((x[0]-rx)*(x[0]-rx)+(y[0]-ry)*(y[0]-ry));
        printf("%.3f %.3f %.3f",rx,ry,r);
    }
    return 0;
}

void gradcut(double *a,double *b,double x1,double x2,double y1,double y2){

    *a=(y2-y1)/(x2-x1);
    *b=y1-*a*x1;
}

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

using namespace std;

double radius(vector<double> center, vector<double> xy){
    double x, y;
    x = xy[0] - center[0];
    y = xy[1] - center[1];
    return sqrt(pow(x,2) + pow(y,2));    
}

vector<double> center(vector<double> coo){
    double a1, b1, c1, a2, b2, c2, x, y;
    a1 = 2 * (coo[2] - coo[0]);
    b1 = 2 * (coo[3] - coo[1]);
    c1 = pow(coo[0],2) - pow(coo[2],2) + pow(coo[1],2) - pow(coo[3],2); 
    
    a2 = 2 * (coo[4] - coo[0]);
    b2 = 2 * (coo[5] - coo[1]);
    c2 = pow(coo[0],2) - pow(coo[4],2) + pow(coo[1],2) - pow(coo[5],2);
    
    x = (b1*c2 - b2*c1) / (a1*b2 - a2*b1);
    y = (c1*a2 - c2*a1) / (a1*b2 - a2*b1);
    
    vector<double> cent = {x,y};
    double rad = radius(cent, coo);
    return {x,y, rad};
    
}



int main(){
    int n;
    vector<double> v = {0,0,0,0,0,0};
    cin >> n;
    while(cin >> v[0] >> v[1] >> v[2] >> v[3] >> v[4] >> v[5]){
        vector<double> c = center(v);
        cout << fixed << setprecision(3) << c[0] << " " << c[1] << " " << c[2] << endl;
    }
}