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 <cstdio>
#include <queue>
#include <algorithm>
#include <cmath>
#define INF 100000000
using namespace std;
#define pw(a) (a)*(a)

int main(){
  double x1,x2,x3,y1,y2,y3;
  int n;
  cin >> n;
  while(n--){
    cin >> x1 >> y1 >> x2 >> y2 >> x3 >> y3;
    double a,b,l,m,n;
    a = -1*(pw(x1) - pw(x2) + pw(y1) - pw(y2));
    b = -1*(pw(x1) - pw(x3) + pw(y1) - pw(y3));
    l = (a*(y1-y3)-b*(y1-y2))/((y1-y3)*(x1-x2)-(x1-x3)*(y1-y2));
    m = ((x1-x3)*a - (x1-x2)*b)/((x1-x3)*(y1-y2)-(y1-y3)*(x1-x2));
    n = -1*(pw(x1) + pw(y1)+ l*x1 + m*y1);
    printf("%.3f %.3f %.3f\n",-l/2.0,-m/2.0,sqrt((pw(l) + pw(m) - 4*n))/2.0);
  }
  return 0;
}

C++: #include <bits/stdc++.h>  
 
using namespace std;
 
#define FOR(i, j, k) for(int i = j; i < k; ++i)
#define rep(i, j) FOR(i, 0, j)
#define repr(i, j) for(int i = j; i >= 0; --i)
#define INF (1 << 30)
 
typedef long long ll;
typedef unsigned long long ull;
typedef pair<int, int> P;

int main() {
	int N;
	scanf("%d", &N);
	rep(c, N) {
		double x1, y1, x2, y2, x3, y3;
		scanf("%lf %lf %lf %lf %lf %lf", &x1, &y1, &x2, &y2, &x3, &y3);
		double p = ((y1-y3)*(y1*y1-y2*y2+x1*x1-x2*x2) - (y1-y2)*(y1*y1-y3*y3+x1*x1-x3*x3))/(2*(y1-y2)*(x1-x2)-2*(y1-y2)*(x1-x3));
		double q = ((x1-x3)*(x1*x1-x2*x2+y1*y1-y2*y2) - (x1-x2)*(x1*x1-x3*x3+y1*y1-y3*y3))/(2*(x1-x2)*(y1-y2)-2*(x1-x2)*(y1-y3));
		double r1 = sqrt( pow( p - x1, 2 ) + pow( q - y1, 2 ) );
        double r2 = sqrt( pow( p - x2, 2 ) + pow( q - y2, 2 ) );
        double r3 = sqrt( pow( p - x3, 2 ) + pow( q - y3, 2 ) );
        double r = ( r1 + r2 + r3 ) / 3.0;
		printf("%.3f %.3f %.3f\n", p, q, r);
	}
	return 0;
}

C++: #include <iostream>
#include <iomanip>
#include <cmath>
using namespace std;
int main()
{
	int n;
	double x1, x2, x3;
	double y1, y2, y3;
	cin >> n;
	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(10) << px << " " << py << " " << r1 <<  endl;
}

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

using namespace std;

int main()
{
    int n;
    cin >> n;
    double x1,y1,x2,y2,x3,y3;
    while(n>0)
    {
        cin >> x1 >> y1 >>x2 >> y2 >> x3 >> y3;
        double s,v1x,v1y,v2x,v2y;
        v1x = y2-y1;
        v1y = x1-x2;

        v2x = y3-y1;
        v2y = x1-x3;
        double detA = v1x*v2y-v1y*v2x;
        double hx = (x2+x1)/2;
        double hy = (y2+y1)/2;
        s = (v2y*(x2-x1)/2 -v2x*(y2-y1)/2)/detA;
        double ox,oy;
        ox = hx + s*v1x;
        oy = hy + s*v1y;
        //if(-0.0005<ox&&ox<0)ox = 0;
        //if(-0.0005<oy&&oy<0)oy = 0;
        double r = sqrt((x1-ox)*(x1-ox)+(y1-oy)*(y1-oy));
        printf("%.3f %.3f %.3f\n",ox,oy,r);
        --n;
    }
    return 0;
}

C++: #include <bits/stdc++.h>
using namespace std;

#define FOR(i,l,r) for(int i = (l);i < (r);i++)
#define ALL(x) (x).begin(),(x).end()
template<typename T> bool chmax(T& a,const T& b){return a < b ? (a = b,true) : false;}
template<typename T> bool chmin(T& a,const T& b){return b < a ? (a = b,true) : false;}
typedef long long ll;

int N;

int main()
{
	double x1,y1,x2,y2,x3,y3;
	scanf("%d",&N);
	FOR(i,0,N){
		scanf("%lf%lf%lf%lf%lf%lf",&x1,&y1,&x2,&y2,&x3,&y3);
		double a = pow(x1 - x2,2.0) + pow(y1 - y2,2.0);
		double b = pow(x2 - x3,2.0) + pow(y2 - y3,2.0);
		double c = pow(x3 - x1,2.0) + pow(y3 - y1,2.0);
		double s = a * (b + c - a) + b * (c + a - b) + c * (a + b - c);
		double x = (a * (b + c - a) * x3 + b * (c + a - b) * x1 + c * (a + b - c) * x2) / s;
		double y = (a * (b + c - a) * y3 + b * (c + a - b) * y1 + c * (a + b - c) * y2) / s;
		printf("%.3f %.3f %.3f\n",x,y,sqrt(pow(x - x1,2.0) + pow(y - y1,2.0)));
	}

	return 0;
}