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<complex>
#include<stdio.h>
#define F(a,b,c) acos((b*b+c*c-a*a)/2/b/c)
int main(){int n;float d,e,f,g,h,i;for(scanf("%d",&n);n--;){scanf("%f%f%f%f%f%f",&d,&g,&e,&h,&f,&i);std::complex<double> a(d,g),b(e,h),c(f,i);float A=abs(b-c),B=abs(c-a),C=abs(a-b),L=F(A,B,C),s=sin(2*L),t=sin(2*F(B,C,A)),u=sin(2*F(C,A,B)),v=s+t+u;printf("%.3f %.3f %.3f\n",(d*s+e*t+f*u)/v,(g*s+h*t+i*u)/v,A/sin(L)/2);}}

C++: #include<iostream>
#include<algorithm>
#include<cstdio>
#include<cmath>
#include<cstdlib>
#include<vector>
#include<string>
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 <complex>
#include <cstdio>
using namespace std;
typedef complex<double> P;

double cross(P a, P b) {
  return (a.real() * b.imag() - a.imag() * b.real());
}
P outcircle(P a,P b,P c){
  return (norm(b-c)*(norm(c-a)+norm(a-b)-norm(b-c))*a+
	  norm(c-a)*(norm(a-b)+norm(b-c)-norm(c-a))*b+
	  norm(a-b)*(norm(b-c)+norm(c-a)-norm(a-b))*c)/(P)(4*cross(b-a,c-a)*cross(b-a,c-a));
}
int main(){
  int n;
  double x1,y1,x2,y2,x3,y3;
  P a,b,c;
  cin>>n;
  for(;n>0;n--){
    cin >>x1 >>y1 >>x2 >>y2 >>x3 >>y3;
    P a=P(x1,y1);
    P b=P(x2,y2);
    P c=P(x3,y3);
    P q = outcircle(a,b,c);
    printf("%.3f %.3f %.3f\n",q.real(),q.imag(),abs(a-q));
  }
  return 0;
}

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

int main(){
	double x1, y1, x2, y2, x3, y3;
	int n;
	double p, q, r;//円の中心を(p, q)、半径をrとする
	
	scanf("%d", &n);
	
	while(n--){
		scanf("%lf%lf%lf%lf%lf%lf", &x1, &y1, &x2, &y2, &x3, &y3);
		
		p = ((pow(x1,2)-pow(x2,2))*(y2-y3)-(pow(x2,2)-pow(x3,2))*(y1-y2)-(y1-y2)*(y2-y3)*(y3-y1)) / (2*((x1-x2)*(y2-y3)-(x2-x3)*(y1-y2)));
		q = ((pow(y1,2)-pow(y2,2))*(x2-x3)-(pow(y2,2)-pow(y3,2))*(x1-x2)-(x1-x2)*(x2-x3)*(x3-x1)) / (2*((y1-y2)*(x2-x3)-(y2-y3)*(x1-x2)));
		r = sqrt(pow(x1-p,2)+pow(y1-q,2));
		
		//p += 0.0005; q += 0.0005; r += 0.0005;
		
		printf("%.3f %.3f %.3f\n", p, q, r);
	}
	return 0;
}

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

const double EPS = 1e-7;
typedef complex<double> P; /* ツ点 */
struct L {                 /* ツ静シツ閉ェ */
	P p, q;
	L(P p, P q) : p(p), q(q) {}
};

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

// ツ陳シツ静シaツづ陳シツ静シbツづ個古ーツ点ツづーツ計ツ算ツつキツづゥツ．ツ静ヲツづ可古ーツ債キツ板サツ津ィツつェツ必ツ須ツ．
P crossPointLL(L a, L b){
	double A = cross(a.q-a.p, b.q-b.p);
	double B = cross(a.q-a.p, a.q-b.p);
	return b.p + B/A * (b.q-b.p);
}

// ツ点pツづ点qツづ個青つ陳シツ禿アツ督卍閉ェツ静シツづーツ陛板つキ
L pointBisector(P p, P q) {
	P cen = (p+q)*0.5;
	return L(cen, cen+(q-p)*P(0,1));
}

int main(){
	int n;
	cin>>n;
	double x1, y1, x2, y2, x3, y3;
	while(cin>>x1>>y1>>x2>>y2>>x3>>y3){
		P p1 = P(x1, y1);
		P p2 = P(x2, y2);
		P p3 = P(x3, y3);
		L l1 = pointBisector(p1, p2);
		L l2 = pointBisector(p2, p3);
		P c = crossPointLL(l1, l2);
		double r = abs(p1-c);
		int x1000 = 1000*c.real()+0.5;
		int y1000 = 1000*c.imag()+0.5;
		int r1000 = 1000*r+0.5;
		printf("%.3f %.3f %.3f", 1.0*x1000/1000, 1.0*y1000/1000, 1.0*r1000/1000);
		cout<<endl;
	}
	return 0;
}