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 <cstdlib>
#include <iostream>
#include <string>
#include <cmath>
#include <algorithm>
#include <vector>
#include <queue>
#include <stack>

using namespace std;
typedef long long ll;

#define PI 3.141592653

int main(){
    int n;
    double x_1,y_1,x_2,y_2,x_3,y_3,x_4,y_4,x_5,y_5,slope_1,slope_2,x,y,r;
    scanf("%d",&n);
    
    for(int i=0;i<n;i++){
        scanf("%lf%lf%lf%lf%lf%lf",&x_1,&y_1,&x_2,&y_2,&x_3,&y_3);
        
        if(y_1 == y_2){
            swap(x_2,x_3);
            swap(y_2,y_3);
        }
        if(y_2 == y_3){
            swap(x_1,x_2);
            swap(y_1,y_2);
        }
        
        slope_1=-(x_1-x_2)/(y_1-y_2);
        slope_2=-(x_3-x_2)/(y_3-y_2);
        
        x_4 = (x_1+x_2)/2;
        y_4 = (y_1+y_2)/2;
        
        x_5 = (x_3+x_2)/2;
        y_5 = (y_3+y_2)/2;

        x = ((slope_1*x_4-slope_2*x_5)-y_4+y_5)/(slope_1-slope_2);
        
        y = slope_1*x-slope_1*x_4+y_4;
        
        r = (x_1-x)*(x_1-x)+(y_1-y)*(y_1-y);
        
        printf("%lf %lf %lf\n",x,y,sqrt(r));
    }
    
    return 0;
}

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


int main(void){

  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 a = sqrt(pow(x2-x1,2) + pow(y2-y1,2));
    double b = sqrt(pow(x3-x2,2) + pow(y3-y2,2));
    double c = sqrt(pow(x3-x1,2) + pow(y3-y1,2));

    double r = a*b*c / sqrt((a+b+c)*(-a+b+c)*(a-b+c)*(a+b-c));

    double A = pow(x2-x1,2) + pow(y2-y1,2);
    double B = pow(x3-x2,2) + pow(y3-y2,2);
    double C = pow(x3-x1,2) + pow(y3-y1,2);
    double s = 4*((x2-x1)*(y3-y1) -(x3-x1)*(y2-y1));
    


    double x = A*(B+C-A) / (2*s);
    double y = B*(C+A-B) / (2*s);

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

  }




  return 0;
}

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

int main(){
  int n;
  double x1, x2, x3, y1, y2, y3, px, py, r, a1, a2, b1, b2, c1, c2;

  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;

    px = (b1 * c2 - b2 * c1) / (a1 * b2 - a2 * b1);
    py = (c1 * a2 - c2 * a1) / (a1 * b2 - a2 * b1);
    r = sqrt((px - x1) * (px - x1) + (py - y1) * (py - y1));

    printf("%.3f %.3f %.3f\n", px, py, r);
  }

  return 0;
}