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 <stdio.h>
#include <string.h>
#include <math.h>
#include <algorithm>
#include <stdlib.h>

using namespace std;
double a, b, c, d, e, f;
double x, y;


void function(){
	if(c/b == f/e){
		x = 0;
		y = c/b;
	}else if(c/a == f/d){
		y = 0;
		x = c/a;
	}else{
		y = (c*d - a*f)/(d*b - a*e);
		x = (c - b*y)/a;
	}
	return;
}


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;

		if((y2-y1) == 0){
			a = 2*(x3 - x1);
			b = 2*(y3 - y1);
			c = (x3 - x1)*(x1 + x3) + (y3 - y1)*(y1 + y3);

			d = 2*(x3 - x2);
			e = 2*(y3 - y2);
			f = (x3 - x2)*(x2 + x3) + (y3 - y2)*(y2 + y3);
		}else if((y3-y1) == 0){

			a = 2*(x2 - x3);
			b = 2*(y2 - y3);
			c = (x2 - x3)*(x2 + x3) + (y2 - y3)*(y2 + y3);

			d = 2*(x2 - x1);
			e = 2*(y2 - y1);
			f = (x2 - x1)*(x1 + x2) + (y2 - y1)*(y1 + y2);
		}else{

			a = 2*(x3 - x1);
			b = 2*(y3 - y1);
			c = (x3 - x1)*(x1 + x3) + (y3 - y1)*(y1 + y3);

			d = 2*(x2 - x1);
			e = 2*(y2 - y1);
			f = (x2 - x1)*(x1 + x2) + (y2 - y1)*(y1 + y2);
		}
		function();
		double r;
		r = sqrt((x - x1)*(x - x1) + (y - y1)*(y - y1));

		printf("%.3lf %.3lf %.3lf",x, y, r);
	}
	return 0;
}

C++: #include <iostream>
#include <complex>
#include <cmath>
using namespace std;

typedef complex<double> point;

#define PI M_PI
#define EPS (1e-10)
#define X real()
#define Y imag()

class Triangle{
private:	
	point a,b,c;
	double edgeA,edgeB,edgeC;
	double angleA,angleB,angleC;
	double calc_angle(double a,double b, double c){
		return acos((b*b+c*c-a*a)/(2.0*b*c));
	}
	bool equal(double a, double b){
		return (abs(a-b) < EPS)? true: false;
	}

public:
	Triangle(point p1,point p2,point p3){
		a=p1; b=p2; c=p3;
		edgeA=abs(b-c);
		edgeB=abs(c-a);
		edgeC=abs(a-b);
		angleA=calc_angle(edgeA,edgeB,edgeC);
		angleB=calc_angle(edgeB,edgeC,edgeA);
		angleC=calc_angle(edgeC,edgeA,edgeB);
	}
	double circumscribed_radius(){
		return (edgeA/(2.0*sin(angleA)));
	}
	double circumscribed_X(){
		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 circumscribed_Y(){
		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(void){
	int x1,y1;
	int x2,y2;
	int x3,y3;
	int n;
	int r,x,y;

	cin >> n;
	for(int i=0;i<n;i++){
		cin >> x1 >> y1 >> x2 >> y2 >> x3 >> y3;
		point a(x1,y1);
		point b(x2,y2);
		point c(x3,y3);
		Triangle Tr(a,b,c);
		r=Tr.circumscribed_radius();
		x=Tr.circumscribed_X();
		y=Tr.circumscribed_Y();
		cout << fixed;
		cout.precision(3);
		cout << r << " " << x << " " << y << endl;
	}
	return 0;
}

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

int main(void){
	int n;
	cin >> n;
	double x1,x2,x3,y1,y2,y3;
	for(int i = 0 ; i < n ; i ++){
		cin>>x1>>y1>>x2>>y2>>x3>>y3;
		double a = x2 * x2 - x1 * x1 + y2 * y2 - y1 * y1;
		double b = x3 * x3 - x1 * x1 + y3 * y3 - y1 * y1;
		double c = 4 * (x2 - x1) * (y3 - y1) - 4 * (x3 - x1) * (y2 - y1);
		
		double x = (2 * (y3 - y1) * a - 2 * (y2 - y1) * b ) / c;
		double y = (-2 * (x3 - x1) * a + 2 * (x2 - x1) * b ) / c;
		double r = sqrt((x - x1) * (x - x1) + (y - y1) * (y - y1));
		
		printf("%.3lf %.3lf %.3lf\n",x,y,r);
		
	} 
	return 0;
}