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;
int main() {
  int n=0;
  double ax,ay,bx,by,cx,cy,S,R,a,b,c,x=0,y=0;
  cin>>n;
  for(int i=0; i<n; i++){
    cin>>ax>>ay>>bx>>by>>cx>>cy;
    S=((bx-ax)*(cy-ay)-(cx-ax)*(by-ay))/2;
    a=sqrt((ax-bx)*(ax-bx)+(ay-by)*(ay-by));
    b=sqrt((cx-bx)*(cx-bx)+(cy-by)*(cy-by));
    c=sqrt((ax-cx)*(ax-cx)+(ay-cy)*(ay-cy));
    cout<<a<<" "<<b<<" "<<c<<" "<<S<<endl;
    R=a*b*c/(4*S);
    x=(a*a*(b*b+c*c-a*a)*ax+b*b*(c*c+a*a-b*b)*bx+c*c*(a*a+b*b-c*c)*cx)/(16*S*S);
    y=(a*a*(b*b+c*c-a*a)*ay+b*b*(c*c+a*a-b*b)*by+c*c*(a*a+b*b-c*c)*cy)/(16*S*S);
    cout<<x<<" "<<y<<" "<<R<<endl;
  }
}

C++: #include <iostream>
#include <iomanip>
#include <cmath>
using namespace std;
int main()
{
	int n;
	double x1, x2, x3;
	double y1, y2, y3;
	cin >> n;
	cin >> x1 >> y1 >> x2 >> y2 >> x3 >> y3;
	double px, py, r;
	double A = (x2 - x1)*(y3 - y2) - (y2 - y1)*(x3 - x2);
	px = 0.5*((y3 - y2)*(x2*x2 - x1*x1 + y2*y2 - y1*y1) - (y2 - y1)*(x3*x3 - x2*x2 + y3*y3 - y2*y2)) / A;
	py = 0.5*(-(x3 - x2)*(x2*x2 - x1*x1 + y2*y2 - y1*y1) + (x2 - x1)*(x3*x3 - x2*x2 + y3*y3 - y2*y2)) / A;
	double a = px - x1;
	double b = py - y1;
	double r0 = (a*a + b*b);
	double r1 = sqrt(r0);
	cout << fixed << setprecision(10) << px << " " << py << " " << r1 <<  endl;
}

C++: #include <iostream>
#include <fstream>
#include <algorithm>
#include <vector>
#include <string>
#include <functional>
#include <array>
#include <stack>
#include <queue>
#include <chrono>
#include <numeric>
#include <memory.h>
#include <map>
#include <math.h>
#include <utility>


#pragma warning(disable:4996)
using namespace std;
#define REP(i,n) for(int i = 0 ; i < n ; ++i)
typedef long long Int;
const double PI = 3.141592653589793238;
const Int INF = 999999999999;
typedef pair<int, int> P;


int main()
{
	int n;
	cin >> n;
	REP(i, n){
		double x1, x2, x3, y1, y2, y3;
		cin >> x1>> x2 >> x3 >> y1 >> y2 >> y3;

		double x21 = x2 - x1;
		double x31 = x3 - x1;
		double y21 = y2 - y1;
		double y31 = y3 - y1;

		double xc = ((y31*(x21*x21 + y21*y21)) - (y21*(x31*x31 + y31*y31))) /
			(2 * (x21*y31 - y21*x31));

		double yc = ((x21*(x31*x31 + y31*y31)) - (x31*(x21*x21 + y21*y21))) /
			(2 * (x21*y31 - y21*x31));	
		
		double d = (xc - x1)*(xc - x1) + (yc - y1)*(yc - y1);
		d = sqrt(d);
		/*
		if (xc < 0){
			xc *= 1000;
			xc -= 0.5;
			floor(xc);
			xc /= 1000;
		}

		if (yc < 0){
			yc *= 1000;
			yc -= 0.5;
			floor(yc);
			yc /= 1000;
		}
		*/
		printf("%.3lf %.3lf %.3lf\n", xc, yc, d);
	}

}

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

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

    scanf("%lf", &n);
    for(int i = 0; i < n; i++){
        scanf("%lf %lf %lf %lf %lf %lf", &x1, &y1, &x2, &y2, &x3, &y3);

        // (x-a)^2+(y-b)^2=r^2$KFM$C9~$`$+?

        a1 = 2 * ( x2 - x1 );
        b1 = 2 * ( y2 - y1 );
        c1 = pow(x1,2) - pow(x2,2) + pow(y1,2) - pow(y2,2);

        a2 = 2 * ( x3 - x1 );
        b2 = 2 * ( y3 - y1 );
        c2 = pow(x1,2) - pow(x3,2) + pow(y1,2) - pow(y3,2);

        px = (b1 * c2 - b2 * c1) / (a1 * b2 - a2 * b1);
        py = (c1 * a2 - c2 * a1) / (a1 * b2 - a2 * b1);
        r = sqrt( pow((px - x1),2) + pow((py - y1),2) );
        printf("%.3f %.3f %.3f\n", px, py, r);
    }

    return 0;
}

C++: #include <bits/stdc++.h>
using namespace std;
class Point{
	public:
	double x,y;
	void input(){
		cin>>x>>y;
	}
};
double dist(Point a,Point b){
	return sqrt(pow(a.x-b.x,2.0)+pow(a.y-b.y,2.0));
}
class Line{
	public:
	double a,b,c;//ax+by=c
	Line(Point s,Point t){
		//x=(x1+x2)/2 , y=(y1+y2)/2????????????
		//??????a=-(x1-x2)/(y1-y2)?????´???
		//(y1-y2)(y-(y1+y2)/2) = -(x1-x2)(x-(x1+x2)/2)
		//(x1-x2)x + (y1-y2)y = (x1^2-x2^2)/2 + (y1^2-y2^2)/2
		a=s.x-t.x;	b=s.y-t.y;
		c=((s.x+t.x)*(s.x-t.x)+(s.y+t.y)*(s.y-t.y))/2.0;
	}
	void multi(double x){
		a*=x;	b*=x;	c*=x;
	}
};
double searchx(Line s,Line t){
	double tmp=s.b;
	s.multi(t.b);	t.multi(tmp);
	return (s.c-t.c)/(s.a-t.a);
}
double searchy(Line s,Line t){
	double tmp=s.a;
	s.multi(t.a);	t.multi(tmp);
	return (s.c-t.c)/(s.b-t.b);
}
int main(){
	int n;	cin>>n;
	while(n--){
		Point a,b,c;
		a.input();	b.input();	c.input();
		Line l(a,b),m(b,c);
		Point center;
		center.x=searchx(l,m);	center.y=searchy(l,m);
		double dis=dist(center,a);
		printf("%.3lf %.3lf %.3lf\n",center.x,center.y,dis);
	}
	return 0;
}