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>
#include <cmath>

using namespace std;

typedef complex<double> Point;

bool eqv(double d1, double d2) {
    return abs(d1-d2) < 1e-10;
}

double r_(double x) {
    if(abs(x) < 0.001) return 0;
    return x;
}

int main() {
    int N;

    cin >> N;
    while(N--) {
        double x1, x2, x3, y1, y2, y3;
        cin >> x1 >> y1 >> x2 >> y2 >> x3 >> y3;
        Point p1(x1, y1), p2(x2, y2), p3(x3, y3);

        //³·è
        double R = abs(abs(p3-p2) / sin(arg(p2-p1) - arg(p3-p1))) / 2;

        Point vb = p3-p2;
        double len = sqrt(R*R - norm(vb)/4.0);
        Point vbh = vb * Point(0, 1);
        Point center = p1 + vb/2.0 + vbh*len/abs(vbh);
        if(eqv(abs(center-p1), R) && eqv(abs(center-p2), R) && eqv(abs(center-p3), R)) {}
        else center = p1 + vb/2.0 - vbh*len/abs(vbh);
        printf("%.3f %.3f %.3f\n", center.real(), center.imag(), R);
    }
    return 0;
}

C++: #include <bits/stdc++.h>
using namespace std;
typedef long double ld;
class Point{
public:
	ld x,y;
};
ld dist(Point a,Point b){
	return sqrt((a.x-b.x)*(a.x-b.x)+(a.y-b.y)*(a.y-b.y));
}
class Line{
public:
	ld a,b,c;//ax+by=c
	Line(Point s,Point t){
		a=s.x-t.x;
		b=s.y-t.y;
		c=(s.x*s.x + s.y*s.y - t.x*t.x - t.y*t.y)/2.0;
	}
	void multi(ld x){
		a*=x;	b*=x;	c*=x;
	}
};
void solve(Line m,Line n,Point s){
	Point ret;
	ld tmp=m.b;
	m.multi(n.b);	n.multi(tmp);
	ret.x=(m.c-n.c)/(m.a-n.a);
	ret.y=(m.c-n.a*ret.x)/(m.b);
	printf("%.15lf %.15lf %.15lf\n",ret.x,ret.y,dist(ret,s));
}

int main(){
	Point s,t,u;	cin>>s.x>>s.y>>t.x>>t.y>>u.x>>u.y;
	Line m(s,t),n(t,u);
	solve(m,n,s);
	return 0;
}

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

using namespace std;

int main()
{
	int n;
	scanf("%d", &n);
	
	for (int i  = 0; i < n; i++){
		double x[3], y[3], s[3];
		double l, m, n;
		
		for (int j = 0; j < 3; j++){
			scanf("%lf %lf", &x[j], &y[j]);
			s[j] = x[j] * x[j] + y[j] * y[j];
		}
		
		double x2[2], y2[2], s2[2];
		x2[0] = x[0] - x[1];
		y2[0] = y[0] - y[1];
		s2[0] = s[0] - s[1];
		x2[1] = x[0] - x[2];
		y2[1] = y[0] - y[2];
		s2[1] = s[0] - s[2];
		
		m = - (s2[0] * x2[1] - s2[1] * x2[0]) / (y2[0] * x2[1] - y2[1] * x2[0]);
		l = - (s2[0] * y2[1] - s2[1] * y2[0]) / (x2[0] * y2[1] - x2[1] * y2[0]);
		n = - s[0] - x[0] * 1 - y[0] * m;
		
		double a,b,r;
		
		a = l / -2;
		b = m / -2;
		r = sqrt(- n - a * a - b * b - l * a - m * b);
		
		printf("%.3lf %.3lf %.3lf\n", a, b, r);
		
		}
	return(0);
}

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

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