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>
#include <chrono>
using namespace std;

using _i64 = int64_t;
using _u64 = uint64_t;
using _f64 = double;

#define _for(i, start, end) for(_i64 i = (_i64)start; i < (_i64)end; ++i)
#define _rep(i, number) _for(i, 0, number)
#define _foreach(e, data) for(auto& e : data)
#define _all(data) data.begin(), data.end()

template<typename type>
_i64 _size(const type& data) { return static_cast<_i64>(data.size()); }
template<typename type, size_t size>
_i64 _size(const type (&)[size]) { return static_cast<_i64>(size); }

enum _flag : bool { able = true, disable = false };

struct _time {
    _time(_flag flag) { check = flag; if(!check) { return; } gettime(start); }
    ~_time() {
        if(!check) { return; }; gettime(end);
        _i64 elapse = chrono::duration_cast<chrono::milliseconds>(end - start).count();
        cout << endl << "Time: " << elapse << " ms" << endl;
    }
    private:
    using _timer = chrono::time_point<chrono::system_clock>;
    _timer start, end; bool check;
    void gettime(_timer& time) { time = chrono::system_clock::now(); }
};

struct _ini { _ini() { ios::sync_with_stdio(false); cin.tie(nullptr); } } _ini;

int main() {
    {
        _time time(disable);
        _f64 n, x1, y1, x2, y2, x3, y3, px, py, r, a, b, c, d, e, f;
        cin >> n;
        _rep(i, n) {
            cin >> x1 >> y1 >> x2 >> y2 >> x3 >> y3;
            a = x1 * 2 - x2 * 2;
            b = y1 * 2 - y2 * 2;
            c = pow(x1, 2) + pow(y1, 2) - pow(x2, 2) - pow(y2, 2);
            d = x2 * 2 - x3 * 2;
            e = y2 * 2 - y3 * 2;
            f = pow(x2, 2) + pow(y2, 2) - pow(x3, 2) - pow(y3, 2);
            px = (c * e - f * b) / (a * e - d * b) + DBL_EPSILON;
            py = (c * d - f * a) / (b * d - e * a) + DBL_EPSILON;
            r = sqrt(pow((px - x1), 2) + pow((py - y1), 2)) + DBL_EPSILON;
            cout << fixed << setprecision(3) << px << " " << py << " " << r << endl;
        }
    }
    return 0;
}

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

double marume( double x ){
	long long t = x * 1000 + ((x > 0) ? 1 : -1) * 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;
		x2 *= 2; y2 *= 2;
		
		double detA = x1 * y2 - y1 * x2;
		double detX = dist1 * y2 - y1 * dist1;
		double detY = x1 * dist2 - dist2 * x1;
		double x = detX / detA; //if(x < 0){ x -= 1e-5; } else { x += 1e-5; }
		double y = detY / detA; //if(y < 0){ y -= 1e-5; } else { y += 1e-5; }
		double r = hypot(x, y) + 1e-7;
		
		x += tx;
		y += ty;
		
		//x = marume(x);
		//y = marume(y);
		//r = marume(r);
		printf("%.3Lf %.3Lf %.3Lf\n", x, y, r);
	}
	return 0;
}

C++: #include <iostream>
#include <cstdio>
#include <cmath>
using namespace std;
int main(){
  double x1,x2,x3,y1,y2,y3;
  int n;
  while(cin >> n){
    for(int i = 0 ; i < n ; i++){
      cin >> x1 >> y1 >> x2 >> y2 >> x3 >> y3; 
      double a = 2*(x2 - x1),b = 2*(y2 - y1),c = x1*x1 - x2*x2 + y1*y1 - y2*y2;
      double a2 = 2*(x3 - x1),b2 = 2*(y3 - y1),c2 = x1*x1 - x3*x3 + y1*y1 - y3*y3;
      double x = (b*c2 - b2*c)/(a*b2 - a2*b);
      double y = (c*a2 - c2*a)/(a*b2 - a2*b);
      double r = sqrt(pow(x-x1,2) + pow(y-y1,2));

      printf("%.3f %.3f %.3f\n",x,y,r);
    }
  }
  return 0;
}

C++: #include<iostream>
#include<cstdio>
#include<math.h>

using namespace std;

int main()
{
	int n;
	double x1,y1,x2,y2,x3,y3,xp,yp,r;
	double a,b,c,d,e,f,L,M,N;
	
	cin>>n;
	for (int i=0; i<n; i++) {
		cin>>x1>>y1>>x2>>y2>>x3>>y3;
		a=x1-x2;
		b=y1-y2;
		c=-1*(x1*x1+y1*y1)+(x2*x2+y2*y2);
		d=x1-x3;
		e=y1-y3;
		f=-1*(x1*x1+y1*y1)+(x3*x3+y3*y3);
		
		M=(c*d-a*f)/(b*d-a*e);
		L=(c-b*M)/a;
		N=-L*x1-M*y1-x1*x1-y1*y1;
		
		xp=-1*(L/2);
		yp=-1*(M/2);
		r=sqrt(-1*N+(L*L)/4+(M*M)/4);
	
		printf("%.3f %.3f %.3f\n",xp,yp,r);
	}
	
	return 0;	
}