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>
#include <algorithm>

using namespace std;

int main() {
    int n;

    scanf("%d", &n);

    double x1, y1, x2, y2, x3, y3;

    while (n--) {
        scanf("%lf %lf %lf %lf %lf %lf", &x1, &y1, &x2, &y2, &x3, &y3);
 
        if (y1 == y3) {
            swap(x3, x2);
            swap(y3, y2);
        }

        if (y2 == y3) {
            swap(x3, x1);
            swap(y3, y1);
        }

        double a = x2 - x3;
        double b = y2 - y3;
        double c = x2 + x3;
        double d = y2 + y3;
        double e = x3 - x1;
        double f = y3 - y1;
        double g = x3 + x1;
        double h = y3 + y1;

        double px = ((a / b) * (c / 2) + d / 2 - (e / f) * (g / 2) - h / 2) / (a / b - e / f);
        double py = -(a / b) * px + (a / b) * c / 2 + d / 2;
        double x = x1 - px;
        double y = y1 - py;
        double r = sqrt(x * x + y * y);

        printf("%.3lf %.3lf %.3lf\n", px, py, r);
    }

    return 0;
}

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;
		cin >> x1 >> y1 >> x2 >> y2 >> x3 >> y3;
		double c1 = (x1 + x2) / 2;
		double c2 = (x1 + x3) / 2;
		double d1 = (y1 + y2) / 2;
		double d2 = (y1 + y3) / 2;
		double k1 = (y2 - y1) / (x2 - x1);
		double k2 = (y3 - y1) / (x3 - x1);
		double py = (c2 - c1 + k2 * d2 - k1 * d1) / (k2 - k1);
		double px = k1 * (d1 - py) + c1;
		double r = sqrt((px - x1)*(px - x1) + (py - y1)*(py - y1));
		cout << setprecision(3);
		cout << fixed;
		cout << px << " " << py << " " << r << endl;
	}
	return 0;
}

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

using namespace std;

int main(void){
	int n;
	double x1,y1,x2,y2,x3,y3,m1,m2,x,y,r;
	double xa,ya,xb,yb,xc,yc;
	cin>>n;
	for(int i=0;i<n;i++){
		cin>>xa>>ya>>xb>>yb>>xc>>yc;
		if(yb==ya){
			x1=xa; y1=ya;
			x2=xc; y2=yc;
			x3=xb; y3=yb;
		} else if(yc==yb){
			x1=xc; y1=yc;
			x2=xa; y2=ya;
			x3=xb; y3=yb;
		} else {
			x1=xc; y1=yc;
			x2=xb; y2=yb;
			x3=xa; y3=ya;
		}
		m1=(x2-x1)/(y2-y1);
		m2=(x3-x2)/(y3-y2);
		x=(1/(m2-m1))*(y3-y1)+(x1+x2)/2*m1-(x2+x3)/2*m2;
		y=(x-(x1+x2)/2)*m1+(y1+y2)/2;
		r=sqrt((x1-x)*(x1-x)+(y1-y)*(y1-y));
		printf("%.3f %.3f %.3f\n",x,y,r);
	}
}

C++: #include <stdio.h>
#include <string>
#include <iostream>
#include <math.h>

using namespace std;

int sosuu(int n);

int main(){
    double x[3]={0};
    double y[3]={0};
    int i=0;
    scanf("%d",&i);
    while(scanf("%lf",&x[0])!=EOF){
        scanf("%lf",&y[0]);
        scanf("%lf",&x[1]);
        scanf("%lf",&y[1]);
        scanf("%lf",&x[2]);
        scanf("%lf",&y[2]);
        
        double a1= 2*(x[1]-x[0]);
        double b1= 2*(y[1]-y[0]);
        double c1= x[0]*x[0]-x[1]*x[1]+y[0]*y[0]-y[1]*y[1];
        
        double a2= 2*(x[2]-x[0]);
        double b2= 2*(y[2]-y[0]);
        double c2= x[0]*x[0]-x[2]*x[2]+y[0]*y[0]-y[2]*y[2];
        
        double xa = (b1*c2-b2*c1)/(a1*b2-a2*b1);
        double ya = (c1*a2-c2*a1)/(a1*b2-a2*b1);
        
        double r =sqrt((xa-x[0])*(xa-x[0])+(ya-y[0])*(ya-y[0]));
        
        printf("%.3lf %.3lf %.3lf\n",xa,ya,r);
        
    }
    
}

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;
}