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>
 
using namespace std;
 
int main(int argc, char **argv)
{
    int n;
    float x1, y1, x2, y2, x3, y3, a1, a2, b1, b2, c1, c2;
    cin >> n;
    while(n--){
        cin >> 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*(y3-y1);
        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("%.3f %.3f %.3f\n", x3, y3, a1);
    }
     
    return 0;
}

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

double marume( double x ){
	long long t = x * 1000 + 0.5;
	return t/1000.0;
}

int main(){
	int n;
	double tx, ty, x1, y1, x2, y2;
	
	cin >> n;
	while(n--){
		cin >> tx >> ty >> x1 >> y1 >> x2 >> y2;
		x1 -= tx; y1 -= ty;
		x2 -= tx; y2 -= ty;
		
		double dist1 = x1 * x1 + y1 * y1;
		double dist2 = x2 * x2 + y2 * y2;
		x1 *= 2; y1 *= 2;
		y1 *= 2; y2 *= 2;
		
		double detA = x1 * y2 - x2 * y1;
		double detX = dist1 * y2 - y1 * dist2;
		double detY = x1 * dist2 - dist1 * x1;
		double x = detX / detA;
		double y = detY / detA;
		double r = hypot(x, y);
		
		x += tx;
		y += ty;
		
		//x = marume(x);
		//y = marume(y);
		//r = marume(r);
		printf("%.3f %.3f %.3f\n", x, y, r);
	}
	return 0;
}

C++: 
// Circumscribed Circle of a Triangle


#include<stdio.h>
#include<iostream>
#include<math.h>
#include<iomanip>
using namespace std;

int main()
{
	int n;
	cin >> n;
	double x[3];
	double y[3];
	double r;

	while(n--){
	 for(int j=0;j<3;j++){
	 	cin >> x[j] >> y[j];
	 }

	 double a = 2*(x[1]-x[0]);
	 double b = 2*(y[1]-y[0]);
	 double c = 2*(x[2]-x[0]);
	 double d = 2*(y[2]-y[0]);

	 double e = pow(x[1],2.0)-pow(x[0],2.0)+pow(y[1],2.0)-pow(y[0],2.0);
	 double f = pow(x[2],2.0)-pow(x[0],2.0)+pow(y[2],2.0)-pow(y[0],2.0);

	 if(a==0){
	 	swap(a,c);
	 	swap(b,d);
	 	swap(e,f);
	 }

	b = b/a;
	e = e/a;
	a = a/a;
	 
	 
	d = d-b*c;
	f = f-e*c;
	c = c-a*c;

	f = f/d;
	d = d/d;

	b = b-d*b;
	e = e-f*b;

	r = sqrt(pow((e-x[0]),2.0)+pow((f-y[0]),2.0));
	
	cout << fixed;
	cout << setprecision(3) << e <<" "<< f << " " << r << endl;
	}
	return 0;

}

C++: #include<cstdio>
#include<cmath>

//#include<iostream>
using namespace std;

int main(){
	int n;
	float x1, y1, x2, y2, x3, y3, a1,b1,c1,a2,b2,c2;
	float xc, yc, r;

	scanf("%d", &n);
	while(n--){
		scanf("%f%f%f%f%f%f",&x1, &y1, &x2, &y2, &x3, &y3);
	
//	http://pegasus.infor.kanazawa-it.ac.jp/~koblab/home/d1504310/acm/asia/1997/97_C_Minimal_Circle.html

    a1=(x2-x1)*2;
    b1=(y2-y1)*2;
    c1=x1*x1-x2*x2+y1*y1-y2*y2;
    a2=(x3-x1)*2;
    b2=(y3-y1)*2;
    c2=x1*x1-x3*x3+y1*y1-y3*y3;
    xc=(b1*c2-b2*c1)/(a1*b2-a2*b1);
    yc=(c1*a2-c2*a1)/(a1*b2-a2*b1);
    r=sqrt((x1-xc)*(x1-xc)+(y1-yc)*(y1-yc));
    printf("%.3f %.3f %.3f\n",xc,yc,r);
		
	}
	return 0;
}