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 <cstdio>
#include <cmath>

using namespace std;

int main() {
    int n;
    double a, b, c, d, e, f;
    double x1, x2, x3, y1, y2, y3, px, py, r;
    cin >> n;
    while (n--) {
        cin >> x1 >> x2 >> x3 >> y1 >> y2 >> y3;
        a = 2 * (x1 - x2);
        b = 2 * (y1 - y2);
        c = x1*x1 + y1*y1 - x2*x2 - y2*y2;
        d = 2 * (x1 - x3);
        e = 2 * (y1 - y3);
        f = x1*x1 + y1*y1 - x3*x3 - y3*y3;
        px = (c*e - b*f) / (a*e - b*d);
        py = (c*d - a*f) / (b*d - a*e);
        r = sqrt(pow(px - x1, 2) + pow(py - y1, 2));
        printf("%.3f %.3f %.3f\n", px, py, r);
    }
    
    return 0;
}

C++: #include<iostream>
#include<algorithm>
#include<cstdio>
#include<cmath>
#include<cstdlib>
#include<vector>
#include<string>
#include<random>
using namespace std;


int main(){

  int n;
  cin >> n;
  double x[3];

  double y[3];

  for(int i=0; i<n; i++){
    cin >> x[0] >> y[0] >> x[1] >> y[1] >> x[2] >> y[2];

    double a, b, c;
    double r, px, py;

    a = sqrt( (x[0]-x[1])*(x[0]-x[1]) + (y[0]-y[1])*(y[0]-y[1]) );
    b = sqrt( (x[1]-x[2])*(x[1]-x[2]) + (y[1]-y[2])*(y[1]-y[2]) );
    c = sqrt( (x[2]-x[0])*(x[2]-x[0]) + (y[2]-y[0])*(y[2]-y[0]) );

    r = (a*b*c) / (sqrt((a+b+c)*(b+c-a)*(a-b+c)*(a+b-c)));
    px = (((x[0]*x[0])+(y[0]*y[0]))*(y[1]-y[2])+((x[1]*x[1])+(y[1]*y[1]))*(y[2]-y[0])
    +((x[2]*x[2])+(y[2]*y[2]))*(y[0]-y[1]))/(x[0]*(y[1]-y[2])+x[1]*(y[2]-y[0])+x[2]*(y[0]-y[1]))/2;

    py = (((x[0]*x[0])+(y[0]*y[0]))*(x[1]-x[2])+((x[1]*x[1])+(y[1]*y[1]))*(x[2]-x[0])
    +((x[2]*x[2])+(y[2]*y[2]))*(x[0]-x[1]))/(y[0]*(x[1]-x[2])+y[1]*(x[2]-x[0])+y[2]*(x[0]-x[1]))/2;


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




  return 0;
}














// EOF

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

typedef complex<double> P;

inline double dot(P a, P b) {return real( conj(a)*b);}
inline double cross(P a, P b) {return imag( conj(a)*b);}

P IntersectionLL(P a1, P a2, P b1, P b2) {
  P a = a2 - a1; P b = b2 - b1;
  return a1 + a * cross(b, b1-a1) / cross(b, a);
}

int main() {
  int T; cin >> T;
  while( T--> 0 ) {
    P p[3];
    for(int i = 0; i < 3; i++) {
      double x, y; cin >> x >> y;
      p[i] = P(x, y);
    }

    P a = p[1] - p[0];
    P b = p[2] - p[0];

    P m1 = p[0] + a / 2.0;
    P m2 = p[0] + b / 2.0;

    P o = IntersectionLL( m1, m1 + a * P(0, 1), m2, m2 + b * P(0, 1) );

    printf("%.3f %.3f %.3f\n", o.real(), o.imag(), abs(o - p[0]) );
  }
}

C++: #include <iostream>
#include <fstream>
#include <algorithm>
#include <vector>
#include <string>
#include <functional>
#include <array>
#include <stack>
#include <queue>
#include <chrono>
#include <numeric>
#include <memory.h>
#include <map>
#include <math.h>
#include <utility>


#pragma warning(disable:4996)
using namespace std;
#define REP(i,n) for(int i = 0 ; i < n ; ++i)
typedef long long Int;
const double PI = 3.141592653589793238;
const Int INF = 999999999999;
typedef pair<int, int> P;


double A[2][2];
double C[2];


int main()
{
	int n;
	cin >> n;
	REP(i, n){
		double x1, x2, x3, y1, y2, y3;
		cin >> x1>> x2 >> x3 >> y1 >> y2 >> y3;

		double x21 = x2 - x1;
		double x31 = x3 - x1;
		double y21 = y2 - y1;
		double y31 = y3 - y1;

		double xc = ((y31*(x21*x21 + y21*y21)) - (y21*(x31*x31 + y31*y31))) /
			(2 * (x21*y31 - y21*x31));

		double yc = ((x21*(x31*x31 + y31*y31)) - (x31*(x21*x21 + y21*y21))) /
			(2 * (x21*y31 - y21*x31));	
		
		double d = (xc - x1)*(xc - x1) + (yc - y1)*(yc - y1);
		double xc_ = xc * 10000;
		double yc_ = yc * 10000;
		xc_ += ((int)xc_ % 10) > 4 ? 10 : (int)-xc_%10;
		yc_ += ((int)yc_ % 10) > 4 ? 10 : (int)-yc_%10;

		printf("%.3lf %.3lf %.3lf\n", xc_/10000, yc_/10000, sqrt(d));


	}

}