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<stdio.h>
#include<iostream>
#include<list>
#include<map>
#include<vector>
#include<algorithm>
#include<string.h>
#include<iomanip>
#include<cmath>
#define range(i,a,b) for(int i = (a); i < (b); i++)
#define rep(i,b) range(i,0,b)
#define debug(x) cout << x << endl;
using namespace std;

int main(){
    double x1, y1, x2, y2, x3, y3;
    double a1, a2, b1, b2, c1, c2;
    double xans, yans, r;
    int n;

    cin >> n;
    rep(i,n){
        cin >> x1 >> y1 >> x2 >> y2 >> x3 >> y3;
        a1 = 2 * (x2 - x1);
        b1 = 2 * (y2 - y1);
        c1 = x1 * x1 - x2 * x2 + y1 * y1 - y2 * y2;
        a2 = 2 * (x3 - x1);
        b2 = 2 * (y3 - y1);
        c2 = x1 * x1 - x3 * x3 + y1 * y1 - y3 * y3;
        xans = (b1 * c2 - b2 * c1) / (a1 * b2 - a2 * b1);
        yans = (c1 * a2 - c2 * a1) / (a1 * b2 - a2 * b1);
        r = sqrt( (x1 - xans) * (x1 - xans) + (y1 - yans) * (y1 - yans) );
        cout << fixed;
        cout << setprecision(3) << xans << " " << yans << " " << r << endl;
    }
}

C++: #include <cstdio>
#include <cmath>
#include <algorithm>
using namespace std;

double jijo(double a){
	return a*a;
}
int main(){
	int n;
	double x1, y1, x2, y2, x3, y3;
	scanf("%d", &n);
	for(int i = 0; i < n; i++){
		scanf("%lf %lf %lf %lf %lf %lf", &x1, &y1, &x2, &y2, &x3, &y3);
		double a1, a2, b1, b2;
		if(y1==y2){y1+=0.0000001;}
		a1 = (x2-x1)/(y1-y2);
		b1 = (y1+y2)/2.0 - a1*(x1+x2)/2.0;
		if(y1==y3){y1+=0.0000001;}
		a2 = (x3-x1)/(y1-y3);
		b2 = (y1+y3)/2.0 - a2*(x1+x3)/2.0;
		double x, y, d;
		x = (b2-b1)/(a1-a2);
		y = a1*x + b1;
		d = sqrt(jijo(x1-x) + jijo(y1-y));
		printf("%.3lf %.3lf %.3lf\n", x, y, d);
	}
	return 0;
}

C++: #include<iostream>
#include<cmath>
using namespace std;
int main(){
	int k;
	double x[3], y[3], a, b, c, d, e, f, l , m, n;
	cin >> k;
	while(k--){
????????????????cin>> x[0] >> y[0] >> x[1] >> y[1] >> x[2] >> y[2];
		
		a = 2 * (x[1] - x[0]);
		b = 2 * (y[1] - y[0]);
		c = ( (x[1]*x[1]) + (y[1]*y[1]) ) -( (x[0]*x[0]) + (y[0]*y[0]) );
		
		d = 2 * (x[2] - x[0]);
		e = 2 * (y[2] - y[0]);
		f = ( (x[2]*x[2]) + (y[2]*y[2]) ) -( (x[0]*x[0]) + (y[0]*y[0]) );
		
		l = (c*e - f*b) / (a*e - d*b);
		m = (c*d - f*a) / (b*d - e*a);
		
		n = sqrt((l - x[0])*(l - x[0]) + (m - y[0])*(m - y[0]));
		
		cout << fixed << setprecision(3) << l << " " << m << " " << n << endl;
	}
}

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 a = 2 * x1 - 2 * x2, b = 2 * y1 - 2 * y2, c = x1 * x1 - x2 * x2 + y1 * y1 - y2 * y2, d = 2 * x1 - 2 * x3, e = 2 * y1 - 2 * y3, f = x1 * x1 - x3 * x3 + y1 * y1 - y3 * y3;
		double px = (c * e - b * f) / (a * e - b * d), py = (a * f - c * d) / (a * e - b * d), r = hypot(x1 - px, y1 - py);
		cout << fixed << setprecision(3) << px << ' ' << py << ' ' << r << endl;
	}
}

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

using namespace std;

int main(void) {
	int ds;
	
	cin >> ds;
	
	for(int i = 0; i < ds; i++) {
		cin.ignore();
		double X[3] = { 0 };
		double Y[3] = { 0 };
		double ans[3] = { 0 };
		
		double a1, b1, c1, a2, b2, c2;
		
		for(int j = 0; j < 3; j++) {
			cin >> X[j] >> Y[j];
		}
		
		a1 = 2 * (X[1] - X[0]);
		b1 = 2 * (Y[1] - Y[0]);
		c1 = X[0] * X[0] - X[1] * X[1] + Y[0] * Y[0] - Y[1] * Y[1];
		
		a2 = 2 * (X[2] - X[0]);
		b2 = 2 * (Y[2] - Y[0]);
		c2 = X[0] * X[0] - X[2] * X[2] + Y[0] * Y[0] - Y[2] * Y[2];
		
		ans[0] = (b1 * c2 - b2 * c1) / (a1 * b2 - a2 * b1);
		ans[1] = (c1 * a2 - c2 * a1) / (a1 * b2 - a2 * b1);
		ans[2] = sqrt( (ans[0] - X[0]) * (ans[0] - X[0]) + (ans[1] - Y[0]) * (ans[1] - Y[0]) );
		
		printf("%.3f %.3f %.3f\n", ans[0], ans[1], ans[2]);
	}
	
	return 0;
}