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 <iostream>
#include <cmath>
using namespace std;
int main(void)
{
    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 a, b, c, A, B, C, s;
        a = sqrt(((x2 - x1) * (x2 - x1)) + ((y2 - y1) * (y2 - y1)));
        b = sqrt(((x3 - x2) * (x3 - x2)) + ((y3 - y2) * (y3 - y2)));
        c = sqrt(((x1 - x3) * (x1 - x3)) + ((y1 - y3) * (y1 - y3)));
        A = a * a;
        B = b * b;
        C = c * c;
        s = (2 * ((A * B) + (B * C) + (C * A))) - ((A * A) + (B * B) + (C * C));
        double px, py, r;
        px = ((x3 * (A * (B + C - A))) / s) + ((x1 * (B * (C + A - B))) / s) + ((x2 * (C * (A + B - C))) / s);
        py = ((y3 * (A * (B + C - A))) / s) + ((y1 * (B * (C + A - B))) / s) + ((y2 * (C * (A + B - C))) / s);
        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);
    }
}

C++: #include <iostream>
#include <stdio.h>
#include <algorithm>
#include <string.h>
#include <complex>
#include <math.h>

using namespace std;
typedef complex<double> Point;

double cross(Point a, Point b) {
  return imag(conj(a) * b); 
}

int main() {
  int test;
  scanf("%d", &test);
  while (test--) {
    double x, y;
    scanf("%lf %lf", &x, &y);
    Point c1 = Point(x, y); 
    scanf("%lf %lf", &x, &y);
    Point c2 = Point(x, y); 
    scanf("%lf %lf", &x, &y);
    Point c3 = Point(x, y); 
    double S = abs(cross(c2 - c1, c3 - c1) / 2.0);
    double a = norm(c3 - c2);
    double b = norm(c1 - c3);
    double c = norm(c2 - c1);
    Point p = (a * (b + c - a) * c1 + b * (c + a - b) * c2 + c * (a + b - c) * c3) / (16.0 * S * S); 
    printf("%.3lf %.3lf %.3lf\n", p.real(), p.imag(), abs(p - c1));
  }
}

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

struct Zahyou
{
	float x, y;
};
Zahyou de[4];

int main()
{
	int n;

	scanf("%d", &n);
	for (int i = 0; i < n; i++)
	{
		for (int j = 1; j < 4; j++)
		{
			scanf("%f %f", &de[j].x, &de[j].y);
		}
		de[0].x = ((de[1].y - de[3].y)*(pow(de[1].y, 2) - pow(de[2].y, 2) + pow(de[1].x, 2) - pow(de[2].x, 2)) + (de[1].y - de[2].y)*(pow(de[1].y, 2) - pow(de[3].y, 2) + pow(de[1].x, 2) - pow(de[3].x, 2))) / (2 * (de[1].y - de[3].y)*(de[1].x - de[2].x) + 2 * (de[1].y - de[2].y)*(de[1].x - de[3].x));
		de[0].y = ((de[1].x - de[3].x)*(pow(de[1].x, 2) - pow(de[2].x, 2) + pow(de[1].y, 2) - pow(de[2].y, 2)) + (de[1].x - de[2].y)*(pow(de[1].x, 2) - pow(de[3].x, 2) + pow(de[1].y, 2) - pow(de[3].y, 2))) / (2 * (de[1].x - de[3].x)*(de[1].y - de[2].y) + 2 * (de[1].x - de[2].x)*(de[1].y - de[3].y));
		
		printf("%.1f %.1f %.3f\n",de[0].x,de[0].y,sqrt(de[0].x+de[0].y));
	}
	return 0;
}

C++: #include<stdio.h>
#include<iostream>
#include<math.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 a1,a2,b1,b2,c1,c2,x,y,r;
         a1=2*(x1-x2);
         b1=2*(y1-y2);
         c1=x1*x1-x2*x2+y1*y1-y2*y2;
         a2=2*(x2-x3);
         b2=2*(y2-y3);
         c2=x2*x2-x3*x3+y2*y2-y3*y3;
         x=(b1*c2-b2*c1)/(a1*b2-a2*b1);
         y=(c1*a2-c2*a1)/(a1*b2-a2*b1);
         r=hypot(x-x1,y-y1);
        printf("%.3lf %.3lf %.3lf\n",x,y,r);
    }
}