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 <stdio.h>
#include <math.h>

int main(void)
{
	double x1, y1, x2, y2, x3, y3;
	double X, Y, r;
	double A1, B1, C1, A2, B2, C2;
	int n;
	int i;
	
	scanf("%d", &n);
	
	for (i = 0; i < n; i++){
		scanf("%lf %lf %lf %lf %lf %lf", &x1, &y1, &x2, &y2, &x3, &y3);
		A1 = 2 * (x2 - x1);
		B1 = 2 * (y2 - y1);
		C1 = x1 * x1 - x2 * x2 + y1 * y1 - y2 * y2;
		A2 = 2 * (x3 - x1);
		B2 = 2 * (x3 - x1);
		C2 = x1 * x1 - x3 * x3 + y1 * y1 - y3 * y3;
		
		X = (B1 * C2 - B2 * C1) / (A1 * B2 - A2 * B1);
		Y = (C1 * A2 - C2 * A1) / (A1 * B2 - A2 * B1);
		
		r = sqrt((X - x1) * (X - x1) + (Y - y1) * (Y - y1));
		
		printf("%.3lf %.3lf %.3lf\n", X, Y, r);
		
	}
	
	return 0;
}

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

int main() {
  int n;
  double x1, y1, x2, y2, x3, y3;
  double a1, b1, c1, a2, b2, c2;
  double x, y, r;
  cin >> n;
  while (n--) {
    cin >> x1 >> y1 >> x2 >> y2 >> x3 >> y3;
    a1 = x2-x1;
    b1 = y2-x1;
    c1 = -a1*(x1+x2)*0.5 - b1*(y1+y2)*0.5;
    
    a2 = x3-x2;
    b2 = y3-y2;
    c2 = -a2*(x2+x3)*0.5 - b2*(y2+y3)*0.5;

    y = (a2*c1-a1*c2)/(a1*b2-a2*b1);
    if (a1) {
      x = -(b1*y+c1)/a1;
    } else {
      x = -(b2*y+c2)/a2;
    }
    r = sqrt((x1-x)*(x1-x) + (y1-y)*(y1-y));

    cout.setf(ios::fixed);
    cout.precision(3);
    cout << x << " " << y << " " << r << endl;
  }
}

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

int
main(void)
{
	char line[80];
	int n;

	if (fgets(line, sizeof line, stdin) == NULL) {
		return 1;
	}
	if (sscanf(line, "%d", &n) != 1) {
		return 1;
	}

	double x1;
	double x2;
	double x3;
	double y1;
	double y2;
	double y3;

	for (int i = 0; i < n; i++) {
		if (fgets(line, sizeof line, stdin) == NULL) {
			return 1;
		}
		if (sscanf(line, "%lf %lf %lf %lf %lf %lf",
				   &x1, &y1, &x2, &y2, &x3, &y3) != 6) {
			return 1;
		}

		double a1 = 2 * (x2 - x1);
		double b1 = 2 * (y2 - y1);
		double c1 = x1*x1 - x2*x2 + y1*y1 - y2*y2;
		double a2 = 2 * (x3 - x1);
		double b2 = 2 * (y3 - y1);
		double c2 = x1*x1 - x3*x3 + y1*y1 - y3*y3;

		double a = sqrt(pow(x2-x3, 2) + pow(y2-y3, 2));
		double b = sqrt(pow(x3-x1, 2) + pow(y3-y1, 2));
		double c = sqrt(pow(x1-x2, 2) + pow(y1-y2, 2));

		double px = (b1*c2 - b2*c1)/(a1*b2 - a2*b1);
		double py = (c1*a2 - c2*a1)/(a1*b2 - a2*b1);
		double r = (a*b*c) / sqrt((a+b+c)*(-a+b+c)*(a-b+c)*(a+b-c));

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

	return 0;
}