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<cstdio>
#include<cmath>
using namespace std;
double x1,Y1,x2,y2,x3,y3;
double px, py,r;
int main()
{
    int n;
    scanf("%d",&n);
    while(n--)
    {
        scanf("%lf%lf%lf%lf%lf%lf",&x1,&Y1,&x2,&y2,&x3,&y3);
        double A1 =(x2*x2+y2*y2-x1*x1-Y1*Y1)*(y3-Y1);
        double B1 =(x3*x3+y3*y3-x1*x1-Y1*Y1)*(y2-Y1);
        double A2 =(x3*x3+y3*y3-x1*x1-Y1*Y1)*(x2-x1);
        double B2 =(x2*x2+y2*y2-x1*x1-Y1*Y1)*(x3-x1);
        double D = (x2-x1)*(y3-Y1)-(y2-Y1)*(x3-x1);
         px=(A1-B1)/D/2;
         py=(A2-B2)/D/2;
         r = sqrt((px-x1)*(px-x1)+(py-Y1)*(py-Y1));
        printf("%.3f %.3f %.3f\n",px,py,r);
    }
    return 0;
}

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

int main ()
{
    int num;
    double x1,y1,x2,y2,x3,y3;

    cin >> num;

    for( int i = 0; i < num; i++ )
    {
        double px = 0, py = 0, r = 0;
        double a, b, c, d, e, f, g;
        cin >> x1 >> y1 >> x2 >> y2 >> x3 >> y3;

        px = ((x1*x1-x3*x3+y1*y1-y3*y3)*(y2-y1)-(x1*x1-x2*x2+y1*y1-y2*y2)*(y3-y1)) / (2*(x2-x1)*(y3-y1)-2*(x3-x1)*(y2-y1));
        
        /*
        a = (x1*x1-x3*x3+y1*y1-y3*y3);
        b = (y2-y1);
        c = (x1*x1-x2*x2+y1*y1-y2*y2);
        d = (y3-y1);
        e = 2*(x2-x1)*(y3-y1);
        f = 2*(x3-x1)*(y2-y1);

        cout << "a: " << a << " b: " << b << " c: " << c << " d: " << d << " e: " << e << " f: " << f << endl;
        g = (a*b-c*d) / (e-f);
        cout << "g: " << g << endl;
        */

        py = ((2*(x1-x2)*px+x2*x2-x1*x1+y2*y2-y1*y1)) / (2*(y2-y1));
        //r = (px-x1)*(px-x1) + (py-y1)*(py-y1);

        cout << fixed;
        cout << setprecision(3) << px << " " << py << " " << sqrt(r) << endl;
    }

    return 0;
}

C++: #include<bits/stdc++.h>
using namespace std;
typedef pair<int,string> P;

int main(){
  int N;
  cin >> N;
  while(N--){
    double x1,y1,x2,y2,x3,y3;
    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 d = 2*(x3-x1),e = 2*(y3-y1),f = x1*x1 - x3*x3 + y1*y1 - y3*y3;
    double x = (b*f - e*c)/(a*e - d*b);
    double y = (c*d - f*a)/(a*e - d*b);
    double r = sqrt((x-x1)*(x-x1) + (y-y1)*(y-y1));
    printf("%.3f %.3f %.3f\n",x,y,r);
  }
}

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

using db = double;

struct poi {
	db x, y;
	void r() { cin >> x >> y; }
	poi operator -(poi p) {
		return {x - p.x, y - p.y};
	}
	poi operator /(db d) {
		return {x / d, y / d};
	}
	db cross(poi p) {
		return x * p.y - y * p.x;
	}
	db len2() {
		return x * x + y * y;
	}
};

poi circum(poi a, poi b, poi c) {
	poi ba = b - a, ca = c - a;
	db lb = ba.len2(), lc = ca.len2(), s = ba.cross(ca);
	return a - poi{ba.y * lc - ca.y * lb,
		ca.x * lb - ba.x * lc} / s / 2;
}

int main() {
	cout << fixed << setprecision(3);
	ios :: sync_with_stdio(false);
	int t; cin >> t;
	while(t --) {
		poi a, b, c;
		a.r(); b.r(); c.r();
		poi o = circum(a, b, c);
		cout << o.x << ' ' << o.y << ' ' << sqrt((o - a).len2()) << '\n';
	}
	return 0;
}

C++: #include<stdio.h>
#include<math.h>
int main(){
    int a;
    scanf("%d",&a);
    while(a--){
        double x1,y1,x2,y2,x3,y3;
        scanf("%lf%lf%lf%lf%lf%lf",&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=hypot(x-x1,y-y1);
        printf("%.3lf %.3lf %.3lf\n",x,y,r);
    }
}

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*hx -v1y*hy)/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;
}