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 <bits/stdc++.h>
#define r(i,n) for(int i=0;i<n;i++)
using namespace std;
typedef double D;
typedef complex<D> P;
typedef vector<P> VP;
P minEnclosingCircle(const VP& ps) {
  P c;
  double move = 0.5;
  r(i,39) {  // 2^(-39-1) \approx 0.9e-12
    r(t,100) {
      D max = 0;
      int k = 0;
      r (j, ps.size()) if (max < norm(ps[j]-c)) {
        max = norm(ps[j]-c);
        k = j;
      }
      c += (ps[k]-c) * move;
    }
    move /= 2;
  }
  return c;
}
int main(){
    int n;
    cin>>n;
    r(i,n){
        VP p;
        D a,b;
        r(j,3){
            cin>>a>>b;
            p.push_back(P(a,b));
        }
        P t=minEnclosingCircle(p);
        D dis=abs(p[0]-t);
        printf("%.3f %.3f %.3f\n",t.real(),t.imag(),dis);
    }
}

C++: #include<iostream>
#include<cstdio>
#include<math.h>
#include<iomanip>
using namespace std;

int main()
{
	int i,n,flg=0;
	double x1,x2,x3,y1,y2,y3;
	double m1,m2,xm1,xm2,ym1,ym2,xo,yo,r;
	//m1,m2…辺の法線　xm1,ym1…辺の中点の座標

	cin>>n;
	for(i=0;i<n;i++){
		cin>>x1>>y1>>x2>>y2>>x3>>y3;

		xm1=(x1+x2)/2;
		xm2=(x2+x3)/2;
		ym1=(y1+y2)/2;
		ym2=(y2+y3)/2;
		if(y1-y2!=0){
			m1=(-1)*(x1-x2)/(y1-y2);
		}else if(y1-y2==0) flg=1;
		if(y2-y3!=0){
			m2=(-1)*(x2-x3)/(y2-y3);
		}else flg=2;
		if(flg==0){
			xo=(m1*xm1-m2*xm2+ym2-ym1)/(m1-m2);
		}else if(flg==1) xo=xm1;
		else if(flg=2) xo=xm2;
		if(flg==1) yo=m2*(xo-xm2)+ym2;
		r=sqrt((x1-xo)*(x1-xo)+(y1-yo)*(y1-yo));
//		cout<<fixed<<setprecision(5)<<m1<<" "<<m2<<endl;
		printf("%.3lf %.3lf %.3lf \n",xo,yo,r);
	}
}

C++: #include "bits/stdc++.h"
using namespace std;

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

C++: #include <iostream>
#include <algorithm>
#include <cstdio>
#include <cmath>
#include <string>
#include <cctype>
#include <stack>
#include <queue>
#include <vector>
#include <cstdlib>
#include <list>
#define _USE_MATH_DEFINES
#include <math.h>

using namespace std;

int main() {

	int n;
	double x1, x2, x3, y1, y2, y3;
	double X, Y, R;
	double a, b, c, d;

	double x[20] = {0}, y[20] = { 0 }, r[20] = { 0 };

	cin >> n;

	for (int i = 0; i < n; i++) {
		cin >> x1 >> y1 >> x2 >> y2 >> x3 >> y3;

		a = x2 - x1;
		b = x3 - x1;
		c = y2 - y1;
		d = y3 - y1;
	
		X = 0.5*((a*a*d - b*b*c) + c*d*(d - c)) / (a*d - b*c);
		Y = 0.5*(a*b*(a - b) + (b*c*c - a*d*d)) / (b*c - a*d);
		R = sqrt(X*X + Y*Y);

		X += x1;
		Y += y1;
		
		//?°???°????¬¬??????????????¨?????\
		if (X > 0)
			X = (int)(X * 1000 + 0.5);
		else X = (int)(X * 1000 - 0.5);

		if (Y>0)
			Y = (int)(Y * 1000 + 0.5);
		else Y = (int)(Y * 1000 - 0.5);

		if (R < 0)
			R = -R;
		R = (int)(R * 1000 + 0.5);
		x[i] = X / 1000;
		y[i] = Y / 1000;
		r[i] = R / 1000;
		
	//	printf("%.3lf %.3lf %.3lf\n", X/1000 , Y /1000, R /1000);
	}

	for (int i = 0; i < n; i++) {
		printf("%.3lf %.3lf %.3lf\n", x[i], y[i], r[i]);
	}

	return 0;
}