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++: /*
 * Problem     : AOJ0010
 * Title       : A New Plan of Aizu Ski Resort (会津山スキー場の新企画)
 * Author      : mizo0203
 * Copyright   : Your copyright free
 * Description : 外接円の中心座標を計算する
 */

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

int n;
double x[3], y[3], xp, yp, r;

void init() {
  scanf("%d", &n);
}

bool input() {
  int i;

  if (!n)
    return false;
  n--;

  for (i = 0; i < 3; i++) {
    scanf("%lf %lf", &x[i], &y[i]);
  }

  return true;
}

int main() {
  double A1, B1, C1, A2, B2, C2;
  init();
  while (input()) {
    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];
    xp = (B1 * C2 - B2 * C1) / (A1 * B2 - A2 * B1);
    yp = (C1 * A2 - C2 * A1) / (A1 * B2 - A2 * B1);
    r = sqrt((x[0] - xp) * (x[0] - xp) + (y[0] - yp) * (y[0] - yp));
    printf("%.3f %.3f %.3f\n", xp, yp, r);
  }

  return 0;
}

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

using namespace std;

double dist(double x1, double y1, double x2, double y2){
	return sqrt((x2-x1)*(x2-x1)+(y2-y1)*(y2-y1));
}

int main(){

	double x[3], y[3];
	int n;

	cin >> n;
	while(n-- > 0){
		for(int i = 0; i < 3; i++){
			cin >> x[i] >> y[i];
		}

		double a = x[1] - x[0];
		double b = y[1] - y[0];
		double c = x[2] - x[1];
		double d = y[2] - y[1];
		double e = x[1]*x[1] - x[0]*x[0] + y[1]*y[1] - y[0]*y[0];
		double f = x[2]*x[2] - x[1]*x[1] + y[2]*y[2] - y[1]*y[1];

		double p = (e*c - f*a) / (2 * (b*c - a*d));
		double q = (e*d - f*b) / (2 * (a*d - b*c));

		double r = dist(x[0], y[0], p, q);

		cout.setf(ios::fixed);
		cout.precision(3);
		cout << p << ' ' << q << ' ' << r << endl;
	}

	return 0;
}

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

using namespace std;

struct Line{
    bool isRightX, isRightY;
    double x, y, a, b;
};

Line getBisector(double x1, double y1, double x2, double y2){
    Line bisector;
    bisector.isRightX = bisector.isRightY = false;
    if ( y1 == y2 ){   
	bisector.isRightY = true;
	bisector.x = ( x1 + x2 ) / 2;
    } else if ( x1 == x2 ){    
	bisector.isRightX = true;
	bisector.y = ( y1 + y2 ) / 2;
    } else {
	bisector.a = ( x2 - x1 ) / ( y1 - y2 );
	bisector.b = ( y1 + y2 ) / 2 - bisector.a * (( x1 + x2 ) / 2);
    }

    return bisector;
}

void compute(){
    double x1, y1, x2, y2, x3, y3, x, y, r;
    cin >> x1 >> y1 >> x2 >> y2 >> x3 >> y3;
    Line AB = getBisector(x1, y1, x2, y2);
    Line AC = getBisector(x1, y1, x3, y3);
    if ( AB.isRightX ){
	if ( AC.isRightY ){
	    x = AC.x; y = AB.y;
	} else {
	    y = AB.y; x = (y - AC.b) / AC.a;
	}
    } else if ( AB.isRightY ){ //y ツ篠イツづ可閉スツ行
	if ( AC.isRightX ){
	    x = AB.x; y = AC.y;
	} else {
	    x = AB.x; y = AC.a * x + AC.b;
	}
    } else {
	if ( AC.isRightX ) {
	    y = AC.y; x = (y - AB.b) / AB.a;
	} else if ( AC.isRightY ) {
	    x = AC.x; y = AB.a * x + AB.b;			
	} else {
	    x = (AC.b - AB.b) / (AB.a - AC.a); 
	    y = AB.a * x + AB.b;
	}	
    }
    r = sqrt( (x - x1)*(x - x1) + (y - y1)*(y - y1) );

    printf("%.3lf %.3lf %.3lf\n", x, y, r);
}

int main(){
    int tcase; cin >> tcase;
    for ( int i = 0; i < tcase; i++ ){
	compute();
    }
    return 0;
}

C++: #include<iostream>
#include<stdio.h>
#include<math.h>
using namespace std;
 struct vect{
    double x,y;
 };
int main(){
  vect a,b,c,p,l1,l2,M1,M2;
  double t1,r;
  int n;
  cin >> n;
  for(int i = 0;i < n;i++){
    cin >> a.x >> a.y >> b.x >> b.y >> c.x >> c.y;
    M1.x = (a.x + b.x) /2;
    M1.y = (a.y + b.y) /2;
    M2.x = (b.x + c.x)/2;
    M2.y = (b.y + c.y)/2;
    l1.y = -(b.x - a.x);
    l1.x = b.y -a.y;
    l2.y = -(c.x-b.x);
    l2.x = c.y -b.y;
    t1 = 1/(-l1.x * l2.y + l2.x * l1.y) *( -l2.y * (M2.x -M1.x) + l2.x * (M2.y -M1.y));
    p.x = M1.x + l1.x * t1;
    p.y = M1.y + l1.y * t1;
    r = sqrt((p.x - a.x)*(p.x - a.x) +(p.y - a.y)*(p.x -a.y));
    printf("%.3f %.3f %.3f\n",p.x,p.y,r);
  }
}