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>
using namespace std;

double det(double a, double b, double c, double d, double e, double f, double g, double h, double i){
	double delta;
	double m[3][3] = {{a, b, c},{d, e, f},{g, h, i}};
	delta = m[0][0]*m[1][1]*m[2][2];
	delta += m[2][0]*m[0][1]*m[1][2];
	delta += m[0][2]*m[1][0]*m[2][1];
	delta -= m[0][2]*m[1][1]*m[2][0];
	delta -= m[0][0]*m[1][2]*m[2][1];
	delta -= m[2][2]*m[0][1]*m[1][0];
	return delta;
}

int main(){
	int n;
	cin >> n;
	for(int i = 0; i < n; i++){
		double x1, y1, x2, y2, x3, y3, x, y, r;
		cin >> x1 >> y1 >> x2 >> y2 >> x3 >> y3;
		double d0 = det(x1, y1, 1, x2, y2, 1, x3, y3, 1);
		double d1 = det((-((x1*x1)+(y1*y1))), y1, 1, (-((x2*x2)+(y2*y2))), y2, 1, (-((x3*x3)+(y3*y3))), y3, 1);
		double d2 = det(x1, (-((x1*x1)+(y1*y1))), 1, x2, (-((x2*x2)+(y2*y2))), 1, x3, (-((x3*x3)+(y3*y3))), 1);
		double d3 = det(x1, y1, (-((x1*x1)+(y1*y1))), x2, y2, (-((x2*x2)+(y2*y2))), x3, y3, (-((x3*x3)+(y3*y3))));
		double l, m, n;
		l = d1 / d0;
		m = d2 / d0;
		n = d3 / d0;
		x = -(l / 2);
		y = -(m / 2);
		r = sqrt((l*l + m*m - (4*n)) / 4);
		printf("%.3f %.3f %.3f\n", x, y, r);
	}
	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;
pair<double,double> A,B,C;
const double EPS = 1e-6,INF = 1e9;

double dist(pair<double,double> a,pair<double,double> b)
{
	double x = a.first - b.first,y = a.second - b.second;
	return sqrt(x * x + y * y);
}

int main()
{
	scanf("%d",&N);
	FOR(i,0,N){
		scanf("%lf%lf%lf%lf%lf%lf",&A.first,&A.second,&B.first,&B.second,&C.first,&C.second);
		pair<double,double> x((A.first + B.first) / 2.0,(A.second + B.second) / 2.0);
		pair<double,double> y((A.first + C.first) / 2.0,(A.second + C.second) / 2.0);
		pair<double,double> ans(INF,INF);
		double p = INF,q = INF,r = INF,s = INF;
		if(abs(A.second - B.second) < EPS){
			ans.first = x.first;
		}
		else{
			p = - (A.first - B.first) / (A.second - B.second);
			q = x.second - x.first * p;
		}
		if(abs(A.second - C.second) < EPS){
			ans.first = y.first;
		}
		else{
			r = - (A.first - C.first) / (A.second - C.second);
			s = y.second - y.first * r;
		}
		assert(p != r);
		if(ans.first == INF){
			ans.first = (s - q) / (p - r);
		}
		if(p != INF){
			ans.second = p * ans.first + q;
		}
		else{
			ans.second = r * ans.first + s;
		}
		printf("%.3f %.3f %.3f\n",ans.first,ans.second,dist(A,ans));
	}

	return 0;
}

C++: #include<iostream>
#include<iomanip>
#include<cmath>
#include<algorithm>
using namespace std;
int t;
double x1,y_1,x2,y2,x3,y3,x,y,r;
int main(){
    cin>>t;
    for(int i=1;i<=t;i++){
        cin>>x1>>y_1>>x2>>y2>>x3>>y3;
        x=((x1*x1+y_1*y_1-x2*x2-y2*y2)/2*(y_1-y3)-(x1*x1+y_1*y_1-x3*x3-y3*y3)/2*(y_1-y2))/(x1*(y2-y3)+x2*(y3-y_1)+x3*(y_1-y2));
        y=((x1*x1+y_1*y_1-x3*x3-y3*y3)/2*(x1-x2)-(x1*x1+y_1*y_1-x2*x2-y2*y2)/2*(x1-x3))/(x1*(y2-y3)+x2*(y3-y_1)+x3*(y_1-y2));
        r=sqrt((x-x1)*(x-x1)+(y-y_1)*(y-y_1));
        cout<<fixed<<setprecision(3)<<x<<" "<<y<<" "<<r<<endl;
    }
    return 0;
}

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

#define SQ(x) ((x) * (x))

int main(void)
{
    int s;
    int i;
    double x1, x2, x3;
    double y1, y2, y3;
    double a, b, c, d, e, f;
    double l, m, n;
    
    scanf("%d", &s);
    for (i = 0; i < s; i++){
        scanf("%lf%lf%lf%lf%lf%lf", &x1, &y1, &x2, &y2, &x3, &y3);
        
        a = (x1 - x2);
        b = (y1 - y2);
        c = -1 * (SQ(x1) - SQ(x2) + SQ(y1) - SQ(y2));
        d = (x1 - x3);
        e = (y1 - y3);
        f = -1 * (SQ(x1) - SQ(x3) + SQ(y1) - SQ(y3));
        
        l = (c * e - b * f) / (e * a - b * d);
        m = (d * c - a * f) / (d * b - e * a);
        
        n = -1 * (SQ(x1) + SQ(y1) + l * x1 + m * y1);
        
        printf("%.3f %.3f %.3f\n", l / -2.0, m / -2.0, sqrt(SQ(l) + SQ(m) - 4 * n) / 2.0);
    }
    
    return (0);
}