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<cmath>
using namespace std;

int main() {
	int n;
	cin >> n;
	for(int i=0;i<n;i++){
		double ax, ay, bx, by, cx, cy;
		cin >> ax >> ay >> bx >> by >> cx >> cy;
		double cs = (by - ay) / (bx - ax);//AB?????????
		double op = -1 / cs;

		double as = (cy - by) / (cx - bx);
		double on = -1 / as;

		double a, b, c, d, e, f;
		a = -1 * op;
		b = 1;
		c = -1 * (op*((ax + bx) / 2)) + ((ay + by) / 2);
		d = -1 * on;
		e = 1;
		f = -1 * (on*((bx + cx) / 2)) + ((by + cy) / 2);
		double any = ((c*d) - (a*f)) / ((b*d) - (a*e));
		double anx = (c - (b*any)) / a;
		double lng = sqrt((abs(anx - bx))*(abs(anx - bx)) + ((abs(any - by)*abs(any - by))));
		
		double aax = round(anx * 10000) / 10000;
		double aay = round(any * 10000) / 10000;
		double alng = round(lng * 10000) / 10000;
		cout << fixed << setprecision(3) << aax << ' ' << aay << ' ' << alng << endl;
	}
	return 0;
}

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,50) {
      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=max(abs(p[0]-t),max(abs(p[1]-t),abs(p[2]-t)));
        printf("%.3f %.3f %.3f\n",t.real(),t.imag(),dis);
    }
}

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

//0010
int main(){
	int n;
	while(cin >> n){
		double x1,y1,x2,y2,x3,y3,x,y,r;

		while(n--){
			cin >> x1 >> y1 >> x2 >> y2 >> x3 >> y3;

			if(x1!=x2){
				x=(x1+x2)/2;
			}else if(x2!=x3){
				x=(x2+x3)/2;
			}else if(x3!=x1){
				x=(x3+x1)/2;
			}
			if(y1!=y2){
				y=(y1+y2)/2;
			}else if(y2!=y3){
				y=(y2+y3)/2;
			}else if(y3!=y1){
				y=(y3+y1)/2;
			}

			r=sqrt(pow(x-x1,2)+pow(y-y1,2));
			cout.setf(ios::fixed);
			cout.precision(3);
			cout << x << " " << y << " " << r << endl;
		}
	}

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

int main(void)
{
    int n;
    double x1, x2, x3, y1, y2, y3;
    cin >> n;
    while (cin >> x1 >> y1 >> x2 >> y2 >> x3 >> y3) {
        double a = 2 * (x1 - x2);
        double b = 2 * (y1 - y2);
        double c = x1*x1 - x2*x2 + y1*y1 - y2*y2;
        double d = 2 * (x1 - x3);
        double e = 2 * (y1 - y3);
        double f = x1*x1 - x3*x3 + y1*y1 - y3*y3;
        double p1 = (e * c - b * f) / (e * a - b * d);
        double p2 = (d * c - a * f) / (d * b - a * e);
        double r = sqrt(pow(x1 - p1, 2) + pow(y1 - p2, 2));
        cout << fixed << std::setprecision(3);
        cout << p1 << " " << p2 << " " << r;
    }
    return 0;
}

C++: #include<stdio.h>
#include<math.h>
double x1, y1, x2, y2, x3, y3;
double px, py;
int main()
{
    int n;
    scanf("%d",&n);
    while(n--)
    {
        scanf("%lf%lf%lf%lf%lf%lf",&x1,&y1,&x2,&y2,&x3,&y3);
        double A1 =(x2*x2+y2*y2-x1*x1-y1*y1)*(y3-y1);
        double B1 =(x3*x3+y3*y3-x1*x1-y1*y1)*(y2-y1);
        double A2 =(x3*x3+y3*y3-x1*x1-y1*y1)*(x2-x1);
        double B2 =(x2*x2+y2*y2-x1*x1-y1*y1)*(x3-x1);
        double D = (x2-x1)*(y3-y1)-(y2-y1)*(x3-x1);
        double X=(double)(A1-B1)/D/2;
        double Y=(double)(A2-B2)/D/2;
        double R = sqrt((X-x1)*(X-x1)+(Y-y1)*(Y-y1));
        printf("%.3f %.3f %.3f\n",X,Y,R);
    }
    return 0;
}