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 <vector>
#include <list>
#include <map>
#include <set>
#include <deque>
#include <stack>
#include <bitset>
#include <algorithm>
#include <functional>
#include <numeric>
#include <utility>
#include <sstream>
#include <queue>
#include <iostream>
#include <iomanip>
#include <cstdio>
#include <complex>
#include <cmath>
#include <cstdlib>
#include <cctype>
#include <string>
#include <cstring>
#include <ctime>
#include <fstream>
#include <stdio.h>

using namespace std;

//conversion
//------------------------------------------
inline int toInt(string s) {int v; istringstream sin(s);sin>>v;return v;}
template<class T> inline string toString(T x) {ostringstream sout;sout<<x;return sout.str();}

//typedef
//------------------------------------------
typedef vector<int> VI;
typedef vector<VI> VVI;
typedef vector<double> VEC;
typedef vector<VEC> MAT;
typedef vector<string> VS;
typedef pair<int, int> PII;
typedef pair<int, PII> TIII;
typedef long long LL;
typedef vector<LL> VLL;
typedef vector<VLL> VVLL;
//container util

//------------------------------------------
#define ALL(a)  (a).begin(),(a).end()
#define RALL(a) (a).rbegin(), (a).rend()
#define PB push_back
#define MP make_pair
#define SZ(a) int((a).size())
#define EACH(i,c) for(typeof((c).begin()) i=(c).begin(); i!=(c).end(); ++i)
#define EXIST(s,e) ((s).find(e)!=(s).end())
#define SORT(c) sort((c).begin(),(c).end())
#define MT(a,b,c) MP(a, MP(b, c))
#define T1 first
#define T2 second.first
#define T3 second.second.first
#define T4 second.second.second

//repetition
//------------------------------------------
#define FOR(i,a,b) for(int i=(a);i<(b);++i)
#define REP(i,n)  FOR(i,0,n)
#define EPS 1.0e-9

int main(){
	int n;
	cin>>n;
	REP(i,n){
		double x[3],y[3];
		REP(j,3)cin>>x[j]>>y[j];
		double a = y[2]-y[1];
		double b = y[0]-y[1];
		double c = (x[0]-x[2])*0.5;
		double d = x[1]-x[2];
		double e = x[1]-x[0];
		double f = (y[0]-y[2])*0.5;
		double s = (c*e-b*f)/(a*e-b*d);
		double rx = (x[1]+x[2])*0.5+s*(y[2]-y[1]);
		double ry = (y[1]+y[2])*0.5+s*(x[1]-x[2]);
		double r = sqrt(pow(rx-x[0], 2.0)+pow(ry-y[0], 2.0));
		printf("%.3f %.3f %.3f\n", rx, ry,r);
	}
	return 0;
}

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

int w(int n)
{
  return n * n;
}

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

  cin >> n;

  for (int i = 0; i < n; i++){
    cin >> x1 >> y1 >> x2 >> y2 >> x3 >> y3;
    double px, py, r; 
    px = ((y1 - y3) * (w(y1) - w(y2) + w(x1) - w(x2)) - (y1 - y2) * (w(y1) - w(y3) + w(x1) - w(x3))) / (2 * (y1 - y3) * (x1 - x2) - 2 * (y1 - y2) * (x1 - x3));
    py = ((x1 - x3) * (w(x1) - w(x2) + w(y1) - w(y2)) - (x1 - x2) * (w(x1) - w(x3) + w(y1) - w(y3))) / (2 * (x1 - x3) * (y1 - y2) - 2 * (x1 - x2) * (y1 - y3));
    r = sqrt(w(px - x1) + w(py - y1));
    
    printf("%.3f %.3f %.3f\n", px, py, r);
  }

  return 0;
}

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

float a, b, c, d, e, f;
float x, y;
float rx, ry;

void solve(){
  float tmp1 = f-(c*d/a);
  float tmp2 = e-(b*d/a);
  y = tmp1/tmp2;
  x = (c - b * y) / a;
  
  rx = x;
  ry = y;
  
  // ツ四ツ偲個古慊禿シ
  int tx = (int)(10000 * x);
  if (tx % 10 >= 5) {
    tx += 10;
  }
  tx /= 10;
  x = (float)tx / 1000.0f;

  int ty = (int)(10000 * y);
  if (ty % 10 >= 5) {
    ty += 10;
  }
  ty /= 10;
  y = (float)ty / 1000.0f;
  
  printf("%.3f %.3f ", x, y);        
}

int main(int argc, char const* argv[]) {
  int n;
  cin>>n;
  for (int i = 0; i < n; i += 1) {
    float x1, y1, x2, y2, x3, y3;
    cin>>x1>>y1>>x2>>y2>>x3>>y3;
    a = -2*x1 + 2*x2;
    b = -2*y1 + 2*y2;
    c = x2*x2 + y2*y2 - x1*x1 - y1*y1;
    d = -2*x1 + 2*x3;
    e = -2*y1 + 2*y3;
    f = x3*x3 + y3*y3 - x1*x1 - y1*y1;

    solve();
    
    float r = (rx - x1)*(rx - x1) + (ry - y1)*(ry - y1);
    r = sqrt(r);
    int tr = (int)(10000 * r);
    if (tr % 10 >= 5) {
      tr += 10;
    }
    tr /= 10;
    r = (float)tr / 1000.0f;
    
    printf("%.3f\n", r);
  }  
  return 0;
}