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 <cstdio>
#include <cmath>

using namespace std;

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

double ix[4], iy[4], x[4], y[4], a[4], b[4], c[4];

void equation(double x1, double y1, double x2, double y2, double *equa, double *equb)
{
  if(x1 == x2){
    *equb = 0;
    return;
  }
  if(y1 == y2){
    *equa = 0;
    return;
  }

  *equa = (y1 - y2) / (x1 - x2);
  return;
}

void line(double cx, double cy, double *equa, double *equb, double *equc)
{
  //  printf("%lf %lf %lf %lf %lf\n", cx, cy, *equa, *equb, *equc);
  if(*equa == 0){
    *equa = 1;
    *equb = 0;
    *equc = cx;
    //    printf("x = %lf\n", *equc);
    return;
  }
  if(*equb == 0){
    *equa = 0;
    *equb = 1;
    *equc = cy;
    //    printf("y = %lf\n", *equc);
    return;
  }

  *equa = -1 / *equa;
  *equc = cy - (*equa) * cx;
  return;
}

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

void point(double a1, double b1, double c1, double a2, double b2, double c2, double *rx, double *ry)
{
  if(!a1 || !b1 || !a2 || !b2 ){
    if(!a1 && !b2){
      *rx = c2;
      *ry = c1;
      return;
    }
    if(!b1 && !a2){
      *rx = c1;
      *ry = c2;
      return;
    }

    if(!a1){
      //      puts("a");
      *ry = c1;
      *rx = ((*ry) - c2) / a2;
      return;
    }
    if(!a2){
      //      puts("a");
      *ry = c2;
      *rx = ((*ry) - c1) / a1;
      return;
    }
    /*    if(!a1 || !a2){
      puts("a");
      double aa = (a1 * b2) - (a2 * b1);
      double cc = (c1 * b2) - (c2 * b1);
      *rx = -(cc / aa);
      *ry = a1 * (*rx) + c1;
      return;
      }*/

    if(!b1){
      //      puts("b1");
      *ry = (a2 * c1 + c2) / b2;
      *rx = a1;
      return ;
    }
    if(!b2){
      //      puts("b2");
      *ry = (a1 * c2 + c1) / b1;
      *rx = a2;
      return;
    }
    /*    if(!b1 || !b2){
      puts("b");
      double bb = (b1 * a2) - (b2 * a1);
      double cc = (c1 * a2) - (c2 * a1);
      *ry = cc / bb;
      *rx = ((*ry) * b1 - c1) / a1;
      return;
      }*/

    fprintf(stderr, "error\n");
    return;
  }

  double bb = (b1 * a2) - (b2 * a1);
  double cc = (c1 * a2) - (c2 * a1);
  *ry = cc / bb;
  *rx = ((*ry) * b1 - c1) / a1;
  return;
}

int main()
{
  int n;
  scanf("%d", &n);
  while(n--){
    for(int i=0;i<3;i++)
      scanf("%lf%lf", &ix[i], &iy[i]);
    //    printf("%lf %lf %lf %lf %lf %lf\n", ix[0], ix[1], ix[2], iy[0], iy[1], iy[2]);    
    a[0] = a[1] = b[0] = b[1] = 1;
    c[0] = c[1] = 0;
    equation(ix[0], iy[0], ix[1], iy[1], &a[0], &b[0]);
    equation(ix[1], iy[1], ix[2], iy[2], &a[1], &b[1]);

    //    printf("傾き %lf %lf %lf %lf\n", a[0], b[0], a[1], b[1]);


    line((ix[0]+ix[1])/2, (iy[0]+iy[1])/2, &a[0], &b[0], &c[0]);
    line((ix[1]+ix[2])/2, (iy[1]+iy[2])/2, &a[1], &b[1], &c[1]);

    //    printf("line %lf %lf %lf %lf %lf %lf\n", a[0], b[0], c[0], a[1], b[1], c[1]);
    
    double resx, resy;
    point(a[0], b[0], c[0], a[1], b[1], c[1], &resx, &resy);

    printf("%.3lf %.3lf %.3lf\n", resx, resy, dist(resx, resy, ix[0], iy[0]));
    //    printf("%lf %lf\n", dist(resx, resy, ix[1], iy[1]), dist(resx, resy, ix[2], iy[2]));
  }
  return 0;
}

C++: #include <iostream>
#include <iomanip>
#include <cmath>
#include <string>
#include <algorithm>

using namespace std;

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;
        
        double a1, a2, b1, b2, c1, c2;
        a1 = (x2 - x1) * 2;
        b1 = (y2 - y1) * 2;
        c1 = x2 * x2  + y2 * y2 - x1 * x1 - y1 * y1;
        a2 = (x3 - x1) * 2;
        b2 = (y3 - y1) * 2;
        c2 = x3 * x3  + y3 * y3 - x1 * x1 - y1 * y1;
        
        double x, y, r;
        x = ((c1 * b2) - (c2 * b1)) / ((a1 * b2) - (a2 * b1));
        y = ((a1 * c2) - (a2 * c1)) / ((a1 * b2) - (a2 * b1));
        r = sqrt((x - x1) * (x - x1) + (y - y1) * (y - y1));
        
        cout << setprecision(3) << fixed << x << " " << y << " " << r << endl;
    }
    
    return 0;
}