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 <vector>
#include <cmath>
#include <iomanip>

using namespace std;

struct point{
    double x;
    double y;
};

struct linear{
    double a;
    double b;
    double c;
};

linear get_linear(point a, point b){
    linear l;

    if(a.x == b.x){
        l.a = 1;
        l.b = 0;
        l.c = a.x;
    }else if(a.y == b.y){
        l.a = 0;
        l.b = 1;
        l.c = a.y;
    }else{
        l.a = (b.x-a.x)/(b.y-a.y);
        l.b = -1;
        l.c = a.x * l.a - a.y;
    }
    return l;
}

linear get_linear_vertical(point p, linear l){
    linear lv;
    lv.a = (-1)*l.b;
    lv.b = l.a;
    lv.c = lv.a*p.x + lv.b*p.y;
    return lv;
}

point get_cross_point(linear l1, linear l2){
    point p;
    p.x = (l1.b*l2.c - l1.c*l2.b)/(l1.b*l2.a - l1.a*l2.b);
    p.y = (l1.c*l2.a - l1.a*l2.c)/(l1.b*l2.a - l1.a*l2.b);
    return p;
}

double point_distance(point s, point e){
    double d;
    d = (e.x - s.x)*(e.x - s.x)+(e.y - s.y)*(e.y - s.y);
    d = sqrt(d);
    return d;
}

int main()
{
    int n;
    double r;
    point p[3], mp, cp;
    linear l1, l2;

    cin >> n;
    vector< point > v[n];
    for(int i = 0; i < n; ++i){
        cin >> p[0].x >> p[0].y >> p[1].x >> p[1].y >> p[2].x >> p[2].y;
        v[i].push_back(p[0]);
        v[i].push_back(p[1]);
        v[i].push_back(p[2]);
    }
    for(int i = 0; i < n; ++i){
        l1 = get_linear(v[i].at(0), v[i].at(1));
        mp.x = (v[i].at(1).x + v[i].at(0).x)/2;
        mp.y = (v[i].at(1).y + v[i].at(0).y)/2;
        l1 = get_linear_vertical(mp, l1);

        l2 = get_linear(v[i].at(0), v[i].at(2));
        mp.x = (v[i].at(2).x + v[i].at(0).x)/2;
        mp.y = (v[i].at(2).y + v[i].at(0).y)/2;
        l2 = get_linear_vertical(mp, l2);

        cp = get_cross_point(l1, l2);
        r = point_distance(v[i].at(0), cp);

        cout << setprecision(3);
        cout << setiosflags(ios::fixed);
        cout << cp.x << ' ' << cp.y << ' ' << r << endl;
    }
    return 0;
}

C++: #include <stdio.h>
#include <math.h>
int main() {int N;scanf("%d",&N);while (N--) {double x1,x2,x3,y1,y2,y3,a1,a2,b1,b2,c1,c2;scanf("%lf %lf %lf %lf %lf %lf",&x1,&y1,&x2,&y2,&x3,&y3);a1=(x2-x1)*2,b1=(y2-y1)*2,a2=(x3-x1)*2,b2=(y3-y1)*2,c1=x1*x1-x2*x2+y1*y1-y2*y2,c2=x1*x1-x3*x3+y1*y1-y3*y3,x3=(b1*c2-b2*c1)/(a1*b2-a2*b1),y3=(c1*a2-c2*a1)/(a1*b2-a2*b1);a1=sqrt((x1-x3)*(x1-x3)+(y1-y3)*(y1-y3));printf("%.3lf %.3lf %.3lf\n",x3,y3,a1);} return 0;}

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

int main()
{
	double x1, y1, x2, y2, x3, y3;
	int n;
	cin >> n;
	double distanceA, distanceB, distanceC, sinA, r, p, q;
	for (int i = 0; i < n; ++i) 
	{
		cin >> x1 >> y1 >> x2 >> y2 >> x3 >> y3;

		distanceA = sqrt((x1 - x3)*(x1 - x3) + (y1 - y3)*(y1 - y3)), distanceB = sqrt((x2 - x3)*(x2 - x3) + (y2 - y3)*(y2 - y3)), distanceC = sqrt((x1 - x2)*(x1 - x2) + (y1 - y2)*(y1 - y2));
	    sinA = sqrt(1.0 - pow((pow(distanceB, 2) + pow(distanceC, 2) - pow(distanceA, 2)) / (distanceB*distanceC * 2), 2));
		r = distanceA / (2 * sinA);
		p = ((y1 - y3)*(y1 * y1 - y2 * y2 + x1 * x1 - x2 * x2) - (y1 - y2)*(y1 * y1 - y3 * y3 + x1 * x1 - x3 * x3)) / (2 * (y1 - y3)*(x1 - x2) - 2 * (y1 - y2)*(x1 - x3));
		q = ((x1 - x3)*(x1 * x1 - x2 * x2 + y1 * y1 - y2 * y2) - (x1 - x2)*(x1 * x1 - x3 * x3 + y1 * y1 - y3 * y3)) / (2 * (x1 - x3)*(y1 - y2) - 2 * (x1 - x2)*(y1 - y3));

		cout << fixed << setprecision(3) << p << " " << q << " " << r << endl;
	}

	return 0;
}

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

int main(void) {
  int i, n, j, k;
  double x1, y1, x2, y2, x3, y3;
  scanf("%d", &n);
  for(i = 0; i < n; ++i) {
    scanf("%lf%lf%lf%lf%lf%lf", &x1, &y1, &x2, &y2, &x3, &y3);
    double xt1 = (x1 + x2) / 2, xt2 = (x3 + x2) / 2, yt1 = (y1 + y2) / 2, yt2 = (y3 + y2) / 2;
    double t1 = y1 - y2, t2 = y2 - y3;
    double x, y, k1, k2;
    if(!t1) {
      x = xt1;
      k2 = (x2 - x3) / (y2 - y3);
      y = k2 * (x - xt2) + yt2;
    } else if(!t2) {
      x = xt2;
      k1 = (x1 - x2) / (y1 - y2);
      y = k1 * (x - xt1) + yt1;
    } else {
      k1 = (x1 - x2) / (y1 - y2), k2 = (x2 - x3) / (y2 - y3);
      x = ((k1 * xt1 - k2 * xt2) - (yt1 - yt2)) / (k1 - k2);
      y = k1 * (x - xt1) + yt1;
    }
    double r = sqrt((x - x1) * (x - x1) + (y - y1) * (y - y1));
    //printf("%f %f %f %f \n", xt1, yt1, xt2, yt2);
    printf("%.3f %.3f %.3f\n", x, y, r);
  }
  return 0;
}