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<math.h>
#include <vector>
using namespace std;

class Triangle{

public:
	double a, b, c;
	double cosA, sinA,R,px,py;

	//con???????§???¢???????????§?¨?????±???????????¬?????¨????????¨????????¨?????°???\???????????????????????£?????????
	double con1, con2, con3,con4,con5,con6;


	Triangle(double x1,double y1,double x2,double y2,double x3,double y3);

	double Radius();
	double Px();
	double Py();

};


//Triangle????????????????????????
Triangle::Triangle(double x1, double y1, double x2, double y2, double x3, double y3){

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

	
	cosA = ((b*b) + (c*c) - (a*a)) / (2 * b*c);
	sinA = sqrt(1 - (cosA*cosA));

	R = a / (2 * sinA);

	//????????¬?????????????????§?¨?????±???????
	con1 = (y3 - y2)*(x1*x1) - (y3 - y1)*(x2*x2) + (y2-y1)*(x3*x3);
	con2 = (y3 - y1)*x2 - (y2 - y1)*x3 + (y2 - y3)*x1;
	con3 = (y1*y1)*(y3 - y2) + (y2*y2)*(y1 - y3) + (y3*y3)*(y2 - y1);

	//????????????con1+2px*con2+con3=0??¨??????
	px = (con3 - con1) / (2 * con2);


	con4 = (x3 - x2)*(y1*y1) - (x3 - x1)*(y2*y2) + (x2 - x1)*(y3*y3);
	con5 = (x3 - x1)*y2 - (x2 - x1)*y3 + (x2 - x3)*y1;
	con6 = (x1*x1)*(x3 - x2) + (x2*x2)*(x1 - x3) + (x3*x3)*(x2 - x1);

	py = (con6 - con4) / (2 * con5);


}


//?????\????????????Radius????±?????????¢??°
double Triangle::Radius(){

	R=round(R*1000)/1000;
	return R;
}

//px???????????¢??°
double Triangle::Px(){

	px = floor(px*1000)/1000;
	return px;
}

//py???????????¢??°
double Triangle::Py(){

	py = floor(py*1000) / 1000;
	return py;
}



//??£??????????????¨???????§£???
int main(void){


	int n;
	double x1, x2, x3, y1, y2, y3;
	cin >> n;

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

		Triangle Triangle(x1, y1, x2, y2, x3, y3);
		
		printf("%.3f ", Triangle.Px());
		printf("%.3f ", Triangle.Py());
		printf("%.3f\n",Triangle.Radius());


	}


	return 0;
}

C++: #include <iostream>
#include <cstdio>
#include <math.h>
using namespace std;

double sq (double x) {return (x * x);}

int main(void)
{
	double x1, x2, x3, y1, y2, y3;
	int num;

	cin >> num;
	for (int i = 0; i < num; i++) {
		cin >> x1 >> y1 >> x2 >> y2 >> x3 >> y3;
                //double a = sqrt(SQ(x2 - x1) + SQ(y2 - y1));
                //double b = sqrt(SQ(x3 - x2) + SQ(y3 - y2));
                //double c = sqrt(SQ(x1 - x3) + SQ(y1 - y3));
                double a = hypot(x2 - x1, y2 -y1);
                double b = hypot(x3 - x2, y3 -y2);
                double c = hypot(x1 - x3, y1 -y3);
                double r = (a * b * c) / sqrt( ( a + b + c ) * ( -1 * a + b + c) * ( a - b + c ) * ( a + b - c ) );


                double xp = ((sq(x1) + sq(y1)) * (y2 - y3) + (sq(x2) + sq(y2)) * (y3 - y1) + (sq(x3) + sq(y3)) * (y1 - y2)) / (x1 * (y2 - y3) + x2 * (y3 - y1) + x3 * (y1 - y2)) / 2;
                double yp = ((sq(x1) + sq(y1)) * (x2 - x3) + (sq(x2) + sq(y2)) * (x3 - x1) + (sq(x3) + sq(y3)) * (x1 - x2)) / (y1 * (x2 - x3) + y2 * (x3 - x1) + y3 * (x1 - x2)) / 2;

                printf("%.3f %.3f %.3f\n", xp, yp, r);
	}

	return 0;
}

C++: #include<iostream>
#include<cstdio>
#include<cmath>
using namespace std;
int main(){
  int n;
  cin >>n;
  while(n--){
    double p[3][2],m[2][2],mi[2][2],det,x[2],o[2];
    for(int i=0; i<3; i++) cin >>p[i][0]>>p[i][1];
    for(int i=1; i<3; i++) for(int j=0; j<2; j++) p[i][j]-=p[0][j];
    for(int i=0; i<2; i++) for(int j=0; j<2; j++) m[i][j] = 2*p[1+i][j];
    for(int i=0; i<2; i++) x[i] = p[i+1][0]*p[i+1][0]+p[i+1][1]*p[i+1][1];
    det = m[0][0]*m[1][1]-m[0][1]*m[1][0];
    mi[0][0] = m[1][1]/det;
    mi[0][1] = -m[0][1]/det;
    mi[1][0] = -m[1][0]/det;
    mi[1][1] = m[0][0]/det;
    for(int i=0; i<2; i++) o[i] = mi[i][0]*x[0]+mi[i][1]*x[1];
    printf("%.3lf %.3lf %.3lf\n",o[0]+p[0][0],o[1]+p[0][1],sqrt(o[0]*o[0]+o[1]*o[1]));
  }
  return 0;
}