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 <cmath>
#include <algorithm>
#include <string>
#include <stdio.h>
using namespace std;
int main(){
    int n;
    cin >> n;
    for(int i=0;i<n;i++){
    double x1,y1,x2,y2,x3,y3;
    cin >> x1 >> y1 >> x2 >> y2 >> x3 >> y3;
    double x,y,r;
    double a,b,c,d,e,f;
    a=2*x1-2*x2;
    b=2*y1-2*y2;
    c=x1*x1-x2*x2+y1*y1-y2*y2;
    d=2*x2-2*x3;
    e=2*y2-2*y3;
    f=x2*x2-x3*x3+y2*y2-y3*y3;
    y=(a*f-c*d)/(a*e-b*d);
    x=(c-b*y)/a;
    r=sqrt((x1-x)*(x1-x)+(y1-y)*(y1-y));
    printf("%.3f %.3f %.3f\n",x,y,r);
    }
}

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

int main(void){
  int n;
  double x1, y1, x2, y2, x3, y3;
  cin >> n;
  for(int i = 0; i < n; i++){
    cin >> x1 >> y1 >> x2 >> y2 >> x3 >> y3;
    double xp1 = x1 - x3, yp1 = y1 - y3, xp2 = x2 - x3, yp2 = y2 - y3;
    double A, B, C;
    double cx, cy, r;
    A = (xp1 / yp1 - xp2 / yp2);
    B = (xp1 * xp1 / yp1 + yp1) / 2;
    C = (xp2 * xp2 / yp2 + yp2) / 2;
    cx = (B - C) / A;
    cy = (xp1 * xp1 / yp1 + yp1) / 2 - cx * xp1 / yp1;
    cx += x3; cy += y3;
    r = hypot(cx - x1, cy - y1);
    printf("%.3lf %.3lf %.3lf\n", cx, cy, r);
  }
  return 0;
}

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

int main(){
	int n;
	double x1,y1,x2,y2,x3,y3,x1_2,x1_3,y1_2,y1_3,z1_2,z1_3,a,b,c,r;
	while(cin >> n){
		for(int i = 0;i < n;++i){
			cin >> x1 >> y1 >> x2 >> y2 >> x3 >> y3;
			z1_2 = (((x1 * x1) + (y1 * y1)) * -1) - (((x2 * x2) + (y2 * y2)) * -1);
			z1_3 = (((x1 * x1) + (y1 * y1)) * -1) - (((x3 * x3) + (y3 * y3)) * -1);
			x1_2 = x1 - x2;
			x1_3 = x1 - x3;
			y1_2 = y1 - y2;
			y1_3 = y1 - y3;
			a = ((y1_2 * z1_3) - (y1_3 * z1_2)) / ((y1_2 * x1_3) - (y1_3 * x1_2)) * -1;
			b = ((x1_2 * z1_3) - (x1_3 * z1_2)) / ((x1_2 * y1_3) - (x1_3 * y1_2)) * -1;
			c = ((x1 * x1) + (y1 * y1) + (a * x1) + (b * y1)) * -1;
			r = sqrt(c * 4 + (a * a) + (b * b));
			printf("%.3f %.3f %.3f\n",a / 2.0,b / 2.0,r);
		}
	}
	return 0;
}

C++: #include <cstdio>
#include <cmath>
#define LOOP(index,times) for(int index=0;index<times;index++)
using namespace std;

int main(){

int n;
float x[3],y[3],detA,a,b,px,py,r;

scanf("%d",&n);

LOOP(i,n){
	scanf("%f %f %f %f %f %f",&x[0],&y[0],&x[1],&y[1],&x[2],&y[2]);

	detA=(x[0]-x[1])*(y[1]-y[2])-(x[1]-x[2])*(y[0]-y[1]);
	a=x[0]*x[0]-x[1]*x[1]+y[0]*y[0]-y[1]*y[1];
	b=x[1]*x[1]-x[2]*x[2]+y[1]*y[1]-y[2]*y[2];
	
	px=0.5/detA*((y[1]-y[2])*a-(y[0]-y[1])*b);
	py=0.5/detA*(-(x[1]-x[2])*a+(x[0]-x[1])*b);
	r=sqrt((px-x[0])*(px-x[0])+(py-y[0])*(py-y[0]));

	printf("%.3f %.3f %.3f\n",px,py,r);
}
return 0;		
}

C++: #include <iostream>
#include <cstdio>
#include <cstring>
#include <algorithm>
#include <complex>
using namespace std;

#define x real()
#define y imag()
typedef complex<double> Point;

Point circumscribed_Circle_Center(Point a, Point b, Point c){
  double A = a.x - b.x;
  double B = a.y - b.y;
  double C = -1 * (a.x*a.x - c.x*c.x + a.y*a.y - b.y*b.y);
  double D = a.x - c.x;
  double E = a.y - c.y;
  double F = -1 * (a.x*a.x - c.x*c.x + a.y*a.y - c.y*c.y);

  double L = (C*E - B*F) / (E*A - B*D);
  double M = (D*C - A*F) / (D*B - E*A);
  double xp = L / -2.0;
  double yp = M / -2.0;
  return (Point(xp, yp));
}

double circumscribed_Circle_Radius(Point a, Point b, Point c){
  double A = a.x - b.x;
  double B = a.y - b.y;
  double C = -1 * (a.x*a.x - c.x*c.x + a.y*a.y - b.y*b.y);
  double D = a.x - c.x;
  double E = a.y - c.y;
  double F = -1 * (a.x*a.x - c.x*c.x + a.y*a.y - c.y*c.y);

  double L = (C*E - B*F) / (E*A - B*D);
  double M = (D*C - A*F) / (D*B - E*A);

  double N = -1 * (a.x*a.x + a.y*a.y + L*a.x + M*a.y);
  double r = sqrt(L*L + M*M - 4*N) / 2.0;
  return r;
}

int main(){
  int n;
  Point a, b, c;
  cin >> n;
  while(n--){
    cin >> a.x >> a.y >> b.x >> b.y >> c.x >> c.y;
    Point C = circumscribed_Circle_Center(a, b, c);
    double r = circumscribed_Circle_Radius(a, b, c);
    printf("%0.3f %0.3f %0.3f\n", C.x, C.y, r);
  }
  return 0;
}