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 <iomanip>
#include <algorithm>
#include <cmath>
#include <string>

#define EPS (1e-8)

using namespace std;

int main() {
  int n;
  double x1, x2, x3, y1, y2, y3;
  double a1, a2, b1, b2, c1, c2;
  double x, y, r;
  cin >> n;
  for (int i = 0; i < n; i++) {
    cin >> x1 >> y1 >> x2 >> y2 >> x3 >> y3;
    a1 = 2*(x2 - x1);
    b1 = 2*(y2 - y1);
    c1 = x1*x1 - x2*x2 + y1*y1 - y2*y2;

    a2 = 2*(x3 - x1);
    b2 = 2*(y3 - y1);
    c2 = x1*x1 - x3*x3 + y1*y1 - y3*y3;

    x = (b1*c2 - b2 * c1) / (a1*b2 - a2*b1) + EPS;
    y = (c1*a2 - c2*a1) / (a1*b2 - a2*b1) + EPS;
    r = sqrt((x-x1)*(x-x1) + (y-y1)*(y-y1)) + EPS;
    cout << fixed << setprecision(3) << x << " " << y << " " << r << endl;
  }
  return 0;
}

C++: #include <cstdio>
#include <cstring>
#include <cmath>
#include <vector>
#include <map>
#include <algorithm>
#include <iostream>
#include <iomanip>

#define rep(i, j) FOR(i, 0, j)
#define FOR(i, j, k) for(int i = j; i < k; ++i)
#define SQ(i) ((i) * (i))
using namespace std;

int main(){
  double x1, y1, x2, y2, x3, y3;
  double a1, b1, c1, a2, b2, c2, x, y, a, b, c, cos_a, sin_a, r;
  int n;
  scanf("%d", &n);
  while(n--){
    scanf("%lf%lf%lf%lf%lf%lf", &x1, &y1, &x2, &y2, &x3, &y3);
    a1 = 2 * (x2 - x1); a2 = 2 * (x3 - x1);
    b1 = 2 * (y2 - y1); b2 = 2 * (y3 - y1);
    c1 = SQ(x1) - SQ(x2) + SQ(y1) - SQ(y2);
    c2 = SQ(x1) - SQ(x3) + SQ(y1) - SQ(y3);
    x = (b1 * c1 - b2 * c1) / (a1 * b2 - a2 * b1);
    y = (c1 * a2 - c2 * a1) / (a1 * b2 - a2 * b1);

    r = SQ(x3-x) + SQ(y3 - y);
    r = sqrt(r);
    printf("%.3f %.3f %.3f\n",x, y, r);
  }
  return 0;
}

C++: #include <iostream>
#include <iomanip>
#include <cmath>
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 c1 = (x1 + x2) / 2;
		double c2 = (x1 + x3) / 2;
		double d1 = (y1 + y2) / 2;
		double d2 = (y1 + y3) / 2;
		double k1 = (y2 - y1) / (x2 - x1);
		double k2 = (y3 - y1) / (x3 - x1);
		double px = (k1 * k2 * (d2 - d1) + c2 * k1 - c1 * k2) / (k1 - k2);
		double py = (c2 - c1 + k2 * d2 - k1 * d1) / (k2 - k1);
		double r = sqrt((px - x1)*(px - x1) + (py - y1)*(py - y1));
		cout << setprecision(3);
		cout << fixed;
		cout << px << " " << py <<" "<<r<< endl;
	}
	return 0;
}

C++: #include<iostream>
#include<cmath>
#include<cstdio>
using namespace std;
int main(){

  double x1,x2,x3,y1,y2,y3;
  int n;
  cin >> n;
  for(int i=0;i<n;i++){
    cin>>x1>>y1>>x2>>y2>>x3>>y3;
    double ax,ay,a,b,c,d,e,f,r;
    if(y2!=y1){
      a=-(x2-x1)/(y2-y1);
      b=-1;
      c=-a*(x1+x2)/2+(y1+y2)/2;
    }else{
      a=1;
      b=0;
      c=(x1+x2)/2;
    }
    if(y3!=y2){
      d=-(x3-x2)/(y3-y2);
      e=-1;
      f=-a*(x2+x3)/2+(y2+y3)/2;
    }else{
      d=1;
      e=0;
      f=(x2+x3)/2;
    }
    ax=(c*e-b*f)/(a*e-b*d);
    ay=(a*f-c*d)/(a*e-b*d);
    if(ax==0)
      ax=0;
    if(ay==0)
      ay=0;
    r=sqrt((x1-ax)*(x1-ax)+(y1-ay)*(y1-ay));
    printf("%0.3f %0.3f %0.3f\n",ax,ay,r);
  }

}

  //y=a(x-a1)+b1
  //y=ax-a*a1+b1
  //ax-y=-a*a1+b1

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

int d(int x1,int y1,int x2,int y2) {
    int k;
    k = sqrt((x1 - x2)*(x1 - x2) + (y1 - y2)*(y1 - y2));
    return k;
}
int main()
{
    int n;
    cin >> n;
    for (int k = 0; k < n; k++) {
        int A[3][2];
        for (int i = 0; i < 3; i++) {
            for (int j = 0; j < 2; j++) {
                cin >> A[i][j];
            }
        }
        cout << d(A[0][0], A[0][1], A[1][0], A[1][1]) << endl;
        cout << d(A[1][0], A[1][1], A[2][0], A[2][1]) << endl;
        cout << d(A[2][0], A[2][1], A[0][0], A[0][1]) << endl;
    }
    
    return 0;
}