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<bits/stdc++.h>
using namespace std;

int main(){

  int n;
  double x1, y1, x2, y2, x3, y3;
  
  cin >> n;
  for(;n--;){
    cin >> x1 >> y1 >> x2 >> y2 >> x3 >> y3;

    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 x = (b1*c2 - b2*c1)/(a1*b2 - a2*b1);
    double y = (c1*a2 - c2*a1)/(a1*b2 - a2*b1);

    double r = sqrt(abs(x1-x)*abs(x1-x) + abs(y1-y)*abs(y1-y));

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

C++: #include <iostream>
#include <iomanip>
#include <cmath>
using namespace std;
int main()
{
	int n;
	double x1, x2, x3;
	double y1, y2, y3;
	cin >> n;
	for (int i = 0; i < n; i++){
		cin >> x1 >> y1 >> x2 >> y2 >> x3 >> y3;
		double px, py, r;
		double A = (x2 - x1)*(y3 - y2) - (y2 - y1)*(x3 - x2);
		px = 0.5*((y3 - y2)*(x2*x2 - x1*x1 + y2*y2 - y1*y1) - (y2 - y1)*(x3*x3 - x2*x2 + y3*y3 - y2*y2)) / A;
		py = 0.5*(-(x3 - x2)*(x2*x2 - x1*x1 + y2*y2 - y1*y1) + (x2 - x1)*(x3*x3 - x2*x2 + y3*y3 - y2*y2)) / A;
		double a = px - x1;
		double b = py - y1;
		double r0 = (a*a + b*b);
		double r1 = sqrt(r0);
		cout << fixed << setprecision(3) << px << " " << py << " " << r1 << endl;
	}
	return 0;
}

C++: #include<bits/stdc++.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 = 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 x = (b1*c2 - b2*c1)/(a1*b2-a2*b1);
    double y = (c1*a2 - c2*a1)/(a1*b2-a2*b1);
    double d = sqrt(fabs(x-x1) * fabs(x-x1) + fabs(y-y1) * fabs(y-y1));
    
    printf("%.3f %.3f %.3f\n",x,y,d);
  }
}

C++: #include <iostream>
#include <string>
#include <vector>
#include <cmath>
#include <algorithm>
#include <cstdlib>
#include <ctime>
#include <stdio.h>

#define MAX 1000000

using namespace std;

int main()
{
	double x1,y1,x2,y2,x3,y3,X1,Y1,X2,Y2,a1,b1,a2,b2;
	double xp,yp,r;
	int n,f;

	cin>>n;
	while(n--){
		cin>>x1>>y1>>x2>>y2>>x3>>y3;
		f=0;

		X1=(x1+x2)/2.0; Y1=(y1+y2)/2.0;
		X2=(x1+x3)/2.0; Y2=(y1+y3)/2.0;
	
		if(y2-y1!=0){
			if(x2!=x1)a1=-(y2-y1)/(x2-x1);
			else a1=0;
			b1=X1*(-a1)+Y1;
		}else f=1;

		if(y3-y1!=0){
			if(x3!=x1)a1=-(y3-y1)/(x3-x1);
			else a2=0;
			b2=X2*(-a2)+Y2;
		}else if(f!=1) f=2;

		if(f==1){ 
			xp=X1;yp=a2*xp+b2;
		}else if(f==2){
			xp=X2; yp=a1*xp+b1;
		}else{
			xp=(b2-b1)/(a1-a2);
			yp=a1*xp+b1;
		}
		r=sqrt((xp-x1)*(xp-x1)+(yp-y1)*(yp-y1));

		printf("%.3f %.3f %.3f\n",xp,yp,r);
	}

	return 0;
}