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 <cmath>
#include <vector>
#include <map>
#include <stack>
#include <queue>
#include <algorithm>
#include <set>

#define FOR(i,a,b) for(int i=(a);i<(b);i++)
#define REP(i,j) FOR(i,0,j)
#define mp std::make_pair

const int INF = 1 << 24;
const int dx[4] = {0, 0, 1, -1}, dy[4] = {1, -1, 0, 0};

typedef unsigned long long ull;

struct P{
    double x, y;
    double size(){
        return std::sqrt(x*x + y*y);
    }
    double sizeS(){
        return x*x + y*y;
    }
    P toUnit(){
        return {x / size(), y / size()};
    }
    P rotate(int angle){
        if(angle == 0){ // 反時計
            return {-y, x};
        }
        return {y, -x};
    }
};

P operator+(const P& lp, const P& rp){
    return {lp.x+rp.x, lp.y+rp.y};
}

P operator-(const P& lp, const P& rp){
    return {lp.x-rp.x, lp.y-rp.y};
}

P operator*(const P& p, const double& k){
    return {k*p.x, k*p.y};
}

double cross(const P& lp, const P& rp){
    return lp.x * rp.y - lp.y * rp.x;
}

double roundOff(double v, int k){
    int i = std::abs(v * pow(10, k)) + 0.5;
    if(v >= 0){
        return 1.0 * i / pow(10, k);
    }
    return -1.0 * i / pow(10, k);
}

int main(){
    int N;
    std::cin >> N;

    REP(i, N){
        P A, B, C, v1, v2, v3;
        std::cin >> A.x >> A.y >> B.x >> B.y >> C.x >> C.y;
        v1 = B - A; v2 = C - A, v3 = B - C;

        double sinA = std::abs(cross(v1, v2)) / (v1.size() * v2.size()),
            r = v3.size() / 2.0 / sinA, k = std::sqrt(r*r-v1.sizeS()/4);

        P m = v1*0.5, p = A + m + m.rotate(cross(A, C) < 0).toUnit() * k;
    
        printf("%.6f\n", p.x * 1000 + 0.5);

        double x = roundOff(p.x, 3), y = roundOff(p.y, 3), R = roundOff(r, 3);
        printf("%.3f %.3f %.3f\n", x, y, R);
    }
}

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

int main() {
	int n;
	std::cin >> n;
	double rax, ray, rbx, rby, rcx, rcy;
	for (int i = 0; i < n; i++) {
		double ax, ay, bx, by, cx, cy, aa, bb, cc, a, b, c, d, e, f, rx, ry, rr;
		std::cin >> rax >> ray >> rbx >> rby >> rcx >> rcy;
		ax = rbx - rax; ay = rby - ray;
		bx = rcx - rbx; by = rcy - rby;
		cx = rax - rcx; cy = ray - rcy;
		std::cerr << ax << " " << bx << " " << cx << std::endl;
		aa = ax * ax + ay * ay;
		bb = bx * bx + by * by;
		cc = cx * cx + cy * cy;
		std::cerr << aa << " " << bb << " " << cc << std::endl;
		a = std::sqrt(aa);
		b = std::sqrt(bb);
		c = std::sqrt(cc);
		std::cerr << a << " " << b << " " << c << std::endl;
		d = aa * (bb + cc - aa);
		e = bb * (cc + aa - bb);
		f = cc * (aa + bb - cc);
		std::cerr << d << " " << e << " " << f << std::endl;
		rx = ((d * rcx) + (e * rax) + (f * rbx)) / (d + e + f);
		ry = ((d * rcy) + (e * ray) + (f * rby)) / (d + e + f);
		rr = (a * b * c) / std::sqrt((a + b + c)*(-a + b + c)*(a - b + c)*(a + b - c));
		std::cout << std::fixed;
		std::cout << std::setprecision(3) << rx << " " << ry << " " << rr << std::endl;
	}

	return 0;
}

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

float round(float val, int d) {
	return (int)(val * pow(10, d) + 0.5) / pow(10,d);
}

int main () {
	int n;
	float x1, x2, x3, y1, y2, y3;
	float m1, m2, b1, b2;
	float x, y, r, hx, hy;
	scanf("%d", &n);
	while (n--) {
		scanf("%f %f %f %f %f %f" , &x1, &y1, &x2, &y2, &x3, &y3);
		if (y1 == y2) {
			x = (x1 + x2) / 2.0;
			m2 = (y3 == y1) ? 0 : (y3 - y1) / (x3 - x1);
			hx = (x1 + x3) / 2.0;
			hy = (y1 + y3) / 2.0;
			b2 = m2 * hx + hy;
			y = -m2 * x + b2;
		} else if (y1 == y3) {
			x = (x1 + x3) / 2.0;
			m1 = (y2 == y1) ? 0 : (y2 - y1) / (x2 - x1);
			hx = (x1 + x2) / 2.0;
			hy = (y1 + y2) / 2.0;
			b1 = m1 * hx + hy;
			y = -m1 * x + b1;
		} else {
			m1 = (x2 == x1) ? 0 : (y2 - y1) / (x2 - x1);
			m2 = (x3 == x1) ? 0 : (y3 - y1) / (x3 - x1);
			hx = (x1 + x2) / 2.0;
			hy = (y1 + y2) / 2.0;
			b1 = m1 * hx + hy;
			hx = (x1 + x3) / 2.0;
			hy = (y1 + y3) / 2.0;
			b2 = m2 * hx + hy;
			x = (b1 - b2) / (m1 - m2);
			y = -m1 * x + b1;
		}
		x = round(x, 3);
		y = round(y, 3);
		r = round(sqrt((x - x1) * (x - x1) + (y - y1) * (y - y1)), 3);
		printf("%.3f %.3f %.3f\n", x, y, r);
	}
	return 0;
}