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>
#include<cmath>
using namespace std;
int main(){
  int n;
  cin >> n;
  for(int i = 0;i<n;i++){
    double x1,y1,x2,y2,x3,y3,a1,b1,c1,a2,b2,c2,x,y,ab;
    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);
    x = ((b1*c2) - (b2 * c1))/((a1 * b2) - (a2 * b1));
    y = ((c1*a2) - (c2 * a1))/((a1 * b2) - (a2 * b1));
    ab = sqrt(((x2 - x) * (x2 - x)) + ((y2 - y) * (y2 - y)));
    cout << fixed << setprecision(3) << x <<" "<< y <<" "<< ab << endl;
  }
}

C++: #include <iostream>
#include <cmath>
#include <iomanip>
using namespace std;
 
int main(){
    cin.tie(0);
    ios::sync_with_stdio(false);
     
    int n;
    cin >> n;
     
    while(n-- > 0){
     
    double x1, y1, x2, y2, x3, y3;
    cin >> x1 >> y1 >> x2 >> y2 >> x3 >> y3;
     
    double a = 2 * (x2 - x1);
    double b = 2 * (y2 - y1);
    double c = x1 * x1 - x2 * x2 + y1 * y1 - y2 * y2;
    double d = 2 * (x3 - x2);
    double e = 2 * (y3 - y2);
    double f = x2 * x2 - x3 * x3 + y2 * y2 - y3 * y3;
         
    double cx = (b * f - c * e)/(a * e - d * b);
    double cy = (a * f - c * d)/(b * d - a * e);
         
    double r = sqrt((x1 - cx)*(x1 - cx) + (y1 - cy)*(y1 - cy));
     
    cout << fixed << setprecision(3) << cx << " " << cy << " " << r << endl;
     
    }
     
    return 0;
}

C++: #include <iostream>
#include <fstream>
#include <algorithm>
#include <vector>
#include <string>
#include <functional>
#include <array>
#include <stack>
#include <queue>
#include <chrono>
#include <numeric>
#include <memory.h>
#include <map>
#include <math.h>
#include <utility>


#pragma warning(disable:4996)
using namespace std;
#define REP(i,n) for(int i = 0 ; i < n ; ++i)
typedef long long Int;
const double PI = 3.141592653589793238;
const Int INF = 999999999999;
typedef pair<int, int> P;


int main()
{
	int n;
	cin >> n;
	REP(i, n){
		double x1, x2, x3, y1, y2, y3;
		cin >> x1>> x2 >> x3 >> y1 >> y2 >> y3;

		double x21 = x2 - x1;
		double x31 = x3 - x1;
		double y21 = y2 - y1;
		double y31 = y3 - y1;
		/*
		double xc = 1.0*((y31*(x21*x21 + y21*y21)) - (y21*(x31*x31 + y31*y31))) /
			(2 * (x21*y31 - y21*x31));

		double yc = 1.0*((x21*(x31*x31 + y31*y31)) - (x31*(x21*x21 + y21*y21))) /
			(2 * (x21*y31 - y21*x31));	
		*/

		double xc = ((y1 - y3)*(y1*y1 - y2*y2 + x1*x1 - x2*x2) - (y1 - y2)*(y1*y1 - y3*y3 + x1*x1 - x3*x3)) / (2 * (y1 - y3)*(x1 - x2) - 2 * (y1 - y2)*(x1 - x3));

		double yc = ((x1 - x3)*(x1 *x1 - x2 *x2 + y1 *y1 - y2 *y2) - (x1 - x2)*(x1*x1  - x3 *x3 + y1 *y1 - y3 *y3) ) / (2*(x1 - x3)*(y1 - y2) - 2*(x1 - x2)*(y1 - y3));

		double d = (xc - x1)*(xc - x1) + (yc - y1)*(yc - y1);
		d = sqrt(d);

		printf("%.3lf %.3lf %.3lf\n", xc, yc, d);
	}
	return 0;
}

C++: #include<iostream>
#include<cstring>
#include<algorithm>
#include<string>
#include<vector>
#include<cstdio>
#include<cmath>
#define pb(in,tmp) in.push_back(tmp)
#define loop(i,a,b) for(int i=a;i<b;i++)
#define rep(i,b) loop(i,0,b)
#define all(in) in.begin(),in.end()
const double PI=acos(-1);
using namespace std;
int main(){
int n;
cin>>n;
rep(i,n){
double a,b,c,d,e,f;
cin>>a>>b>>c>>d>>e>>f;
double x,y,r;
double p,q,s,t,u,v,w,z;
p=b-f;
q=e-a;
s=(a+c)/2;
t=(b+f)/2;

u=b-d;
w=(a+c)/2;
v=c-a;
z=(b+d)/2;

x=(v*p*w-u*p*z-u*p*s+u*p*t)/(v*p-u*q);
if(u)y=v*(x-w)/u+z;
else y=q*(x-s)/p+t;
r=hypot(x-a,y-b);

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