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>
using namespace std;

double get_num(double x){
	x = x * 1000;
	if(x >= 0){
		x = (int)(x + 0.5);
		return ((double)x / 1000);
	} else {
		x = (int)(x - 0.5);
		return ((double)x / 1000);
	}
}

int main()
{
	int n;
	cin >> n;
	for(int i = 0; i < n; i++){
		double x1, y1;
		double x2, y2;
		double x3, y3;
		double m12x, m12y;
		double m13x, m13y;
		double dx12, dy12;
		double dx13, dy13;
		double c12, c13;
		double xp, yp;
		double r;
		cin >> x1 >> y1 >> x2
			>> y2 >> x3 >> y3;
		m12x = (x1 + x2) / 2;
		m12y = (y1 + y2) / 2;
		m13x = (x1 + x3) / 2;
		m13y = (y1 + y3) / 2;
		dx12 = x2 - x1;
		dy12 = y2 - y1;
		dx13 = x3 - x1;
		dy13 = y3 - y1;
		c12 = m12x * dx12 + m12y * dy12;
		c13 = m13x * dx13 + m13y * dy13;
		yp = (c12 * dx13 - c13 * dx12) / (dy12 * dx13 - dy13 * dx12);
		if(dx12 == 0){
			xp = (c13 - (dy13 * yp)) / dx13;
		}else{
			xp = (c12 - (dy12 * yp)) / dx12;
		}
		r = sqrt((xp - x1) * (xp - x1) + ((yp - y1) * (yp - y1)));
		xp = get_num(xp);
		yp = get_num(yp);
		r = get_num(r);
		cout << fixed << setprecision(3) << xp << " " << yp << " " << r << endl;

	}
	return 0;
}

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

int main()
{
	int n;
	double x1,x2,x3,y1,y2,y3,x,y,r;
	double a,b,c;
	scanf("%d",&n);
	for(int i=0;i<n;i++){
		scanf("%lf%lf%lf%lf%lf%lf",&x1,&x2,&x3,&y1,&y2,&y3);
	    x=(y1-y3)*(y1*y1-y2*y2+x1*x1-x2*x2)-(y1-y2)*(y1*y1-y3*y3+x1*x1-x3*x3);
	    x/=(2*(y1-y3)*(x1-x2)-2*(y1-y2)*(x1-x3));
	 
	    y=(x1-x3)*(x1*x1-x2*x2+y1*y1-y2*y2)-(x1-x2)*(x1*x1-x3*x3+y1*y1-y3*y3);
	    y/=(2*(x1-x3)*(y1-y2)-2*(x1-x2)*(y1-y3));

		c=sqrt((x1-x3)*(x1-x3)+(y1-y3)*(y1-y3));
		b=sqrt((x3-x2)*(x3-x2)+(y3-y2)*(y3-y2));
		a=sqrt((x2-x1)*(x2-x1)+(y2-y1)*(y2-y1));
		r=a*b*c/sqrt((a+b+c)*(-a+b+c)*(a-b+c)*(a+b-c));
		printf("%.3f %.3f %.3f\n",x,y,r);
	}
	return 0;
}
/*?????\???*/

C++: #include<iostream>
#include<stdio.h>
#include<math.h>
#include<string>
#include<algorithm>
#include<utility>
using namespace std;
double zeti(double);
int main() {
	pair<double, double> a;
	pair<double, double> b;
	pair<double, double> c;
	pair<double, double> m1;
	pair<double, double> m2;
	double s1, s2,x1,y1,x2,y2,x,y,b1,b2;
	int n;
	scanf("%d", &n);
	for (int i = 0; i < n; ++i) {
		x = -1000.0;
		y = -1000.0;
		b1 = 0.0;
		b2 = 0.0;
		s1 = -1000.0;
		s2 = -1000.0;
		scanf("%lf%lf", &a.first, &a.second);
		scanf("%lf%lf", &b.first, &b.second);
		scanf("%lf%lf", &c.first, &c.second);
		m1.first = (a.first + b.first) / 2.0;
		m1.second = (a.second + b.second) / 2.0;
		m2.first = (b.first + c.first) / 2.0;
		m2.second = (b.second + c.second) / 2.0;
		swap(m1.first, m1.second);
		swap(m2.first, m2.second);
		//x is qual
		if (a.first - b.first == 0) {
			x = m1.first;
			b1 = m1.first;
		}
		//y is qual
		else if (a.second - b.second == 0) {
			y = m1.second;

		}
		else {
			s1 = (zeti(a.second - b.second)) / (zeti(a.first - b.first));
			b1 = s1*m1.first - m1.second;
		}
		//x is qual
		if (b.first - c.first == 0) {
			x = m2.first;
			b2 = m1.first;
		}
		//y is qual
		else if (b.second - c.second == 0) {
			y = m2.second;
		}
		else {
			s2 = (zeti(c.second - b.second)) / (zeti(c.first - b.first));
			b2 = s2*m2.first - m2.second;
		}
			s1 = 1.0 / s1*-1.0;
			s2 = 1.0 / s2*-1.0;

		if (x == -1000.0) {
			x = (b1 - b2) / (s2 - s1);
		}
		if (y==-1000.0&&s1 ==0.001) {
			y = s2*x + b2;
		}
		else if(y == -1000.0&&s2 == 0.001) {
			y = s1*x + b1;
		}
		double r,w,e;
		w = zeti(a.first - x);
		e = zeti(a.second - y);
		r = sqrt(w*w+e*e);
		printf("%.3lf %.3lf %.3lf\n", x, y,r);

	}
	return 0;
}
double zeti(double center) {
	if (center < 0) {
		center *= -1;
	}
	return center;
}