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 <iomanip>
#include <math.h>
using namespace std;

#define L 0.00001

typedef struct {
	double x, y;
} P;
typedef struct {
	double a, b, c;
} EQ;

int n;
P p[3];
double r;

inline bool is0(double d) {
	return d < L && d > -L;
}

inline EQ get_eq(P p1, P p2) {
	return{ p2.y - p1.y, p1.x - p2.x, (p2.y - p1.y)*p1.x - (p2.x - p1.x)*p1.y };
}

inline P get_center(P p1, P p2) {
	return{ (p1.x + p2.x) / 2, (p1.y + p2.y) / 2 };
}

inline EQ conv_ra(EQ eq, P p) {
	return{ eq.b, -eq.a, eq.b*p.x - eq.a*p.y };
}

inline P get_p(EQ eq1, EQ eq2) {
	double y;
	if (is0(eq1.a)) {
		y = eq1.c / eq1.b;
		return{ (eq2.c - eq2.b*y) / eq2.a,y };
	}
	else if (is0(eq2.a)) {
		y = eq2.c / eq2.b;
		return{ (eq1.c - eq1.b*y) / eq1.a,y };
	}
	else {
		y = (eq1.c*eq2.a - eq2.c*eq1.a) / (eq1.b*eq2.a - eq2.b - eq1.a);
		return{ (eq1.c - eq1.b*y) / eq1.a,y };
	}
}

inline double dist(P p1, P p2) {
	return sqrt(pow((p1.x - p2.x), 2) + pow(p1.y - p2.y, 2));
}

inline EQ get_ieq(P p1, P p2) {
	return conv_ra(get_eq(p1, p2), get_center(p1, p2));
}

inline double rnd(double d) {
	int a = d * 10000;
	if (a % 10 >= 5) {
		a += 10;
	}
	a /= 10;
	return a * 0.001;
}

int main(){
	cin >> n;
	EQ eq1, eq2;
	P c;
	double r;
	for (int I = 0; I < n; I++) {
		for (int i = 0; i < 3; i++) {
			cin >> p[i].x >> p[i].y;
		}
	}
	eq1 = get_ieq(p[0], p[1]);
	eq2 = get_ieq(p[1], p[2]);
	c = get_p(eq1, eq2);
	r = dist(c, p[0]);
	cout << fixed << setprecision(3) << rnd(c.x) << " " << rnd(c.y) << " " << rnd(r) << endl;

	return 0;
}

C++: #include<cstdio>
#include<cmath>
/*
px2-2pxx1+x12+py2-2pyy1+y12=px2-2pxx2+x22+py2-2pyy2+y22
x12+y12-2(pxx1+pyy1)=x22+y22-2(pxx2+pyy2)
x12+y12-2(pxx1+pyy1)=x32+y32-2(pxx3+pyy3)
2px(x2-x1)+2py(y2-y1)=x22+y22-x12-y12
2px(x3-x1)+2py(y3-y1)=x32+y32-x12-y12
px=((x22+y22-x12-y12)(y3-y1)-(x32+y32-x12-y12)(y2-y1))/2((x2-x1)(y3-y1)-(x3-x1)(y2-y1))
py=(x22+y22-x12-y12-2px(x2-x1))/2(y2-y1)*/
int main(){
    int n;
    scanf("%d", &n);
    while(n--){
        float x1, x2, x3, y1, y2, y3; 
        scanf("%f %f %f %f %f %f", &x1, &y1, &x2, &y2, &x3, &y3);
        float px, py; 
        px=((x2*x2+y2*y2-x1*x1-y1*y1)*(y3-y1)-(x3*x3+y3*y3-x1*x1-y1*y1)*(y2-y1))/(2*((x2-x1)*(y3-y1)-(x3-x1)*(y2-y1)));
        if(y2!=y1)
             py=(x2*x2+y2*y2-x1*x1-y1*y1-2*px*(x2-x1))/(2*(y2-y1));
        else
            py=(x3*x3+y3*y3-x1*x1-y1*y1-2*px*(x3-x1))/(2*(y3-y1));
        float r;
        r=sqrt((px-x1)*(px-x1)+(py-y1)*(py-y1));
        printf("%.3f %.3f %.3f\n", px, py, r); 
    }   
    return 0;
}

C++: #include <iostream>
#include <cmath>
#include <cstdio>
using namespace std;

int w(int n)
{
  return n * n;
}

int main()
{
  double x1, y1, x2, y2, x3, y3;
  int n;
  double a, b, c;
  double px, py, r;

  cin >> n;

  for (int i = 0; i < n; i++){
    cin >> x1 >> y1 >> x2 >> y2 >> x3 >> y3;

    a = sqrt(w(x1 - x2) + w(y1 - y2));
    b = sqrt(w(x2 - x3) + w(y2 - y3));
    c = sqrt(w(x3 - x1) + w(y3 - y1));
    px = ((y1 - y3) * (w(y1) - w(y2) + w(x1) - w(x2)) - (y1 - y2) * (w(y1) - w(y3) + w(x1) - w(x3))) / (2 * (y1 - y3) * (x1 - x2) - 2 * (y1 - y2) * (x1 - x3));
    py = ((x1 - x3) * (w(x1) - w(x2) + w(y1) - w(y2)) - (x1 - x2) * (w(x1) - w(x3) + w(y1) - w(y3))) / (2 * (x1 - x3) * (y1 - y2) - 2 * (x1 - x2) * (y1 - y3));
    r = (a * b * c) / sqrt((a + b + c) * (b + c - a) * (a - b + c) * (a + b - c));
    
    printf("%.3f %.3f %.3f\n", px, py, r);
  }

  return 0;
}