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 <cmath>
#include <iomanip>

using namespace std;

int main() {
    int n;
    double x1, x2, x3, y1, y2, y3;
    double a, b, c, sinA, xa, ya, r;
    double cosA, cosB, cosC;

    cin >> n;
    for(int i = 0; i < n; i++) {
        cin >> x1 >> y1 >> x2 >> y2 >> x3 >> y3;

        a = sqrt(pow(x2 - x3, 2) + pow(y2 - y3,2));
        b = sqrt(pow(x1 - x3, 2) + pow(y1 - y3,2));
        c = sqrt(pow(x2 - x1, 2) + pow(y2 - y1,2));

        cosA = (pow(b, 2) + pow(c, 2) - pow(a, 2)) / (2 * b * c);
        cosB = (pow(c, 2) + pow(a, 2) - pow(b, 2)) / (2 * c * a);
        cosC = (pow(a, 2) + pow(b, 2) - pow(c, 2)) / (2 * a * b);

        sinA = sqrt(1.0 - pow(cosA, 2));

        xa = (a * cosA * x1 + b * cosB * x2 + c * cosC * x3) / (a * cosA + b * cosB + c * cosC);
        ya = (a * cosA * y1 + b * cosB * y2 + c * cosC * y3) / (a * cosA + b * cosB + c * cosC);
        r = a / (2.0 * sinA);

        cout << fixed << setprecision(3) << xa << " " << ya << " " << r << endl;
    }
}

C++: #include<iostream>
#include<cstdio>
#include<cmath>
using namespace std;
int main()
{
long n,i;
double x1,y1,x2,y2,x3,y3,Px,Py,r,a1,b1,c1,a2,b2,c2;
cin>>n;
for(i=0;i<n;i++){
cin>>x1>>y1>>x2>>y2>>x3>>y3;
a1=(x2-x1)*2;
b1=(y2-y1)*2;
c1=x1*x1-x2*x2+y1*y1-y2*y2;
a2=(x3-x1)*2;
b2=(y3-y1)*2;
c2=x1*x1-x3*x3+y1*y1-y3*y3;
Px=(b1*c2-b2*c1)/(a1*b2-a2*b1);
Py=(c1*a2-c2*a1)/(a1*b2-a2*b1);
r=sqrt((x1-x)*(x1-x)+(y1-y)*(y1-y));
printf("%.3f %.3f %.3f\n",Px,Py,r);
}
return 0;
}

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

using namespace std;

typedef complex<double> Point;
#define sq(x) (pow((x), (2.0)))
#define X real()
#define Y imag()

class Triangle{
    private:
        Point a, b, c;
        double edgeA, edgeB, edgeC;
        double angleA, angleB, angleC;
        double getAngle(double a, double b, double c){
            return acos((sq(b) + sq(c) - sq(a)) / (2.0 * b * c));
        }
    public:
        Triangle(Point p1, Point p2, Point p3){
            a = p1;
            b = p2;
            c = p3;
            edgeA = abs(b - c);
            edgeB = abs(a - c);
            edgeC = abs(a - b);
            angleA = getAngle(edgeA, edgeB, edgeC);
            angleB = getAngle(edgeB, edgeC, edgeA);
            angleC = getAngle(edgeC, edgeA, edgeB);
        }
        double circleRadius(){
            return (edgeA / sin(angleA)/ 2.0);
        }
        double circleX(){
            double A = sin(2.0 * angleA);
            double B = sin(2.0 * angleB);
            double C = sin(2.0 * angleC);
            return ((a.X * A + b.X * B + c.X * C) / (A+B+C));
        }
        double circleY(){
            double A = sin(2.0 * angleA);
            double B = sin(2.0 * angleB);
            double C = sin(2.0 * angleC);
            return ((a.Y * A + b.Y * B + c.Y * C) / (A+B+C));
        }
};

int main(){
    int n;
    double x1, y1, x2, y2, x3, y3;
    double r, xp, yp;
    scanf("%d", &n);
    for(int i = 0; i < n; ++i){
        scanf("%lf %lf %lf %lf %lf %lf",
                &x1, &y1, &x2, &y2, &x3, &y3);
        Point a(x1, y1);
        Point b(x2, y2);
        Point c(x3, y3);
        Triangle T(a, b, c);
        r = T.circleRadius();
        xp = T.circleX();
        yp = T.circleY();
        printf("%.3f %.3f %.3f\n", xp, yp, r);
    }
    return 0;
}

C++: #include <math.h>
#include <stdio.h>
 
int main()
{
    double x1,x2,x3,y1,y2,y3,r,xp,yp;
    int n,i;
    scanf("%d",&n);
    for(i=1;i<=n;i++){
        scanf("%lf%lf%lf%lf%lf%lf",&x1,&y1,&x2,&y2,&x3,&y3);
        xp=((y1-y2)*(x3*x3+y3*y3)+(y2-y3)*(x1*x1+y1*y1)+(y3-y1)*(x2*x2+y2*y2))/(2*(x1*(y2-y3)+x2*(y3-y1)+x3*(y1-y2)));
        yp=((x1-x2)*(x3*x3+y3*y3)+(x2-x3)*(x1*x1+y1*y1)+(x3-x1)*(x2*x2+y2*y2))/(2*(y1*(x2-x3)+y2*(x3-x1)+y3*(x1-x2)));
        r=sqrt((x1-xp)*(x1-xp)+(y1-yp)*(y1-yp));
        printf("%.3lf %.3lf %.3lf\n",xp,yp,r);
    }
    return 0;
}