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 <iomanip>
using namespace std;

void OutputCentralCoodinateAndRadius(double x1, double y1, double x2, double y2, double x3, double y3)
{
	double x, y, r;
	if(y1 == y2 || y2 == y3 || y3 == y1){
		if(y2 == y3){
			swap(x3, x1);
			swap(y3, y1);
		}else if(y3 == y1){
			swap(x2, x3);
			swap(y2, y3);
		}
		double xa = (x2 + x3) / 2;
		double ya = (y2 + y3) / 2;
		double a  = (-x3 + x2) / (y3 - y2);
		x = (x1 + x2) / 2;
		y = a * (x - xa) + ya;
	}else{
		double xa = (x1 + x2) / 2;
		double ya = (y1 + y2) / 2;
		double a  = (-x2 + x1) / (y2 - y1);
		double xb = (x2 + x3) / 2;
		double yb = (y2 + y3) / 2;
		double b  = (-x3 + x2) / (y3 - y2);
		x = (b * xb - a * xa - yb + ya) / (b - a);
		y = a * (x - xa) + ya;
	}
	r = sqrt((x - x1) * (x - x1) + (y - y1) * (y - y1));
	cout << fixed << setprecision(3) << x << ' ' << y << ' ' << r << endl;
}

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;
		OutputCentralCoodinateAndRadius(x1, y1, x2, y2, x3, y3);
	}
	return 0;
}

C++: #include <iostream>
#include <iomanip>
#include <math.h>
using namespace std;

int main(void){
    int n;
    double x1, x2, x3, y1, y2, y3, Px, Py, r;
    cin >> n;
    
    for(int i=1; i<=n; i++){
        cin >> x1 >> y1 >> x2 >> y2 >> x3 >> y3;
    
        Px = ( (x1*x1 + y1*y1 - x3*x3 - y3*y3) / (2 * (y1-y3)) - (x2*x2 + y2*y2 - x3*x3 - y3*y3) / (2 * (y2-y3)) ) / ( (x1-x3)/(y1-y3) - (x2-x3)/(y2-y3) );
        Py = -(x1-x3) / (y1-y3) * Px + (x1*x1 + y1*y1 - x3*x3 - y3*y3) / (2 * (y1-y3));
        
        r = sqrt((x1-Px)*(x1-Px) + (y1-Py)*(y1-Py));

        cout << fixed << setprecision(3) << Px << " " << Py << " " << r << endl;
    }
    return 0;
}

C++: 
#include <iostream>
 #include <math.h>
 #include <string>
using namespace std;

int main() {
	int n;
	cin>>n;
	for(int h=0;h<n;h++){
double x1,y1,x2,y2,x3,y3,x2m,x3m,y2m,y3m,x21,y21,x31,y31,xy21,xans,yans;
cin>>x1>>y1>>x2>>y2>>x3>>y3;
	x2m=(x1+x2)/2;
	y2m=(y1+y2)/2;
	x3m=(x1+x3)/2;
	y3m=(y1+y3)/2;
	x21=x2-x1;
	x31=x3-x1;
	y21=y2-y1;
	y31=y3-y1;
	
	
if(y1!=y2){
	xy21=x21/y21;
	xans=(x31*x3m-y31*(xy21*x2m+y3m-y2m))/(x31-y31*xy21);
	yans=-xy21*(xans-x2m)+y2m;
}	
else{
	xans=x2m;
	yans=(x3m-xans)*x31/y31+y3m;
}
double r;
r=sqrt((xans-x1)*(xans-x1)+(yans-y1)*(yans-y1));
double x=xans,y=yans;
if(x<0.0004&& x>-0.0004) x=0.000;
if(y<0.0004&& y>-0.0004) y=0.000;

	printf("%.3f %.3f %.3f\n",x,y,r);
}

	return 0;
}

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

int main(){
    double x1,y1,x2,y2,x3,y3;
    int n;
    cin >> n;
    double a,b,c;
    double ans1,ans2;
    for(int i=0;i<n;i++){
        double ans = 0;
        cin >> x1 >> y1 >> x2 >> y2 >> x2 >> x3 >> y3;
        a = hypot(x2 - x1,y2 - y1);
        b = hypot(x3 - x1,y3 - y1);
        c = hypot(x3 - x2,y3 - y2);
        ans = (a*b*c) / (sqrt((a+b+c)*(b+c-a)*(a-b+c)*(a+b-c)));
        ans1 = (((x1*x1)+(y1*y1))*(y2-y3)+((x2*x2)+(y2*y2))*(y3-y1)+((x3*x3)+(y3*y3))*(y1-y2))/(x1*(y2-y3)+x2*(y3-y1)+x3*(y1-y2))/2;
        ans2 = (((x1*x1)+(y1*y1))*(x2-x3)+((x2*x2)+(y2*y2))*(x3-x1)+((x3*x3)+(y3*y3))*(x1-x2))/(y1*(x2-x3)+y2*(x3-x1)+y3*(x1-x2))/2;
        printf("%.3f %.3f %.3f\n",ans1,ans2,ans);
    }
}

C++: #include <iostream>
#include <iomanip>
#include <math.h>
using namespace std;
int main()
{
	int n;
	cin >> n;
	while (n--)
	{
		double x1, y1, x2, y2, x3, y3;
		cin >> x1 >> y1 >> x2 >> y2 >> x3 >> y3;
		double a1, b1, c1, a2, b2, c2;
		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;
		double x, y, r;
		x = (b1 * c2 - b2 * c1) / (a1 * b2 - a2 * b1);
		y = (c1 * a2 - c2 * a1) / (a1 * b2 - a2 * b1);
		r = sqrt((x1 - x)*(x1 - x) + (y1 - y)*(y1 - y));
		cout << fixed << std::setprecision(3) << x << " " << y << " " << r << "\n";
	}

	return 0;
}