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<stdio.h>
#include<math.h>
int main(){
	double ax,ay,bx,by,cx,cy,ix,iy,r;
	double abx,aby,acx,acy;
	double fb,fc;
	double ffb,ffc,aaby,aacy;
	int n,a;
	scanf("%d",&n);
	for(a=0;a<n;a++){
		scanf("%lf %lf",&ax,&ay);
		scanf("%lf %lf",&bx,&by);
		scanf("%lf %lf",&cx,&cy);
		abx=bx-ax;
		aby=by-ay;
		acx=cx-ax;
		acy=cy-ay;
		fb=abx*abx+aby*aby;
		fc=acx*acx+acy*acy;
		ffb=fb*acx;
		ffc=fc*abx;
		aaby=aby*acx;
		aacy=acy*abx;
		iy=(ffc-ffb)/((aacy-aaby)*2);
		if(abx!=0){ix=(fb-(2*iy*aby))/(abx*2);}
		if(acx!=0){ix=(fc-(2*iy*acy))/(acx*2);}
		r=sqrt(ix*ix+iy*iy);
		ix=ix+ax;
		iy=iy+ay;
		printf("%.3lf %.3lf %.3lf\n",ix,iy,r);
	}
	return 0;
}

C++: #include <math.h>
#include <stdio.h>

int main() {
    double x1, x2, x3, y1, y2, y3;
    int n;
    scanf("%d", &n);
    while (n--) {
        scanf("%lf%lf%lf%lf%lf%lf", &x1, &y1, &x2, &y2, &x3, &y3);
        double a,b,c,d,e,f,x,y,r;
        a=2*(x2-x1);
        b=2*(y2-y1);
        c=x2*x2+y2*y2-x1*x1-y1*y1;
        d=2*(x3-x2);
        e=2*(y3-y2);
        f=x3*x3+y3*y3-x2*x2-y2*y2;
        x=(b*f-e*c)/(b*d-e*a);
        y=(d*c-a*f)/(b*d-e*a);
        r=sqrt((x-x1)*(x-x1)+(y-y1)*(y-y1));
        printf("%.3lf %.3lf %.3lf\n", x, y, r);
    }
    return 0;
}

C++: #include <iostream>
#include <iomanip>
#include <algorithm>
#include <cmath>
#include <string>

using namespace std;

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

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

    x *= 1000;
    y *= 1000;
    r *= 1000;

    x += 0.5;
    y += 0.5;
    r += 0.5;

    cout << fixed << setprecision(3) << ((double)((int)x))/1000 << " " << ((double)((int)y))/1000 << " " << ((double)((int)r))/1000 << endl;
  }
  return 0;
}

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

double sqnorm(double x1, double y1, double x2, double y2) {
    return pow((x1 - x2), 2) + pow((y1 - y2), 2);
}

int main(void) {
    int N; cin >> N;
    double x1, y1, x2, y2, x3, y3;
    double lsq, msq, nsq, l, n;
    double cos, a, b, c, d, e, f, det;
    double r, px, py;
    for(int i = 0; i < N; i++) {
        cin >> x1 >> y1 >> x2 >> y2 >> x3 >> y3;
        lsq = sqnorm(x1, y1, x2, y2);
        msq = sqnorm(x2, y2, x3, y3);
        nsq = sqnorm(x3, y3, x1, y1);
        l = sqrt(lsq);
        n = sqrt(nsq);
        cos = (msq + nsq - lsq) / (2.0 * sqrt(msq * nsq));
        r = sqrt(lsq / (4.0 * (1.0 - cos * cos)));
        a = (x2 - x1) / l;
        b = (y2 - y1) / l;
        c = (x3 - x1) / n;
        d = (y3 - y1) / n;
        e = l / 2.0;
        f = n / 2.0;
        det = a* d - b * c;
        px = (d * e - b * f) / det + x1;
        py = (-c * e + a * f) / det + y1;
        r = roundf(r * 1000.0) / 1000.0;
        px = roundf(px * 1000.0) / 1000.0;
        py = roundf(py * 1000.0) / 1000.0;
        printf("%.3f %.3f %.3f\n", px, py, r);
    }
}

C++: #include <iostream>
#include <stdio.h>
#include <string>
#include <math.h>
#include <algorithm>
using namespace std;
int main(){
  double x1, y1, x2, y2, x3, y3;
  double px, py;
  double r;
  double M1, mx1, my1;
  double M2, mx2, my2;
  int n;
  cin >> n;

  while(1){
    if(n == 0) break;

    cin >> x1 >> y1 >> x2 >> y2 >> x3 >> y3;

    mx1 = (x1 + x2) / 2;
    my1 = (y1 + y2) / 2;
    if(y1 - y2 == 0) M1 = 0;
    else  M1 = (-1)*(x1 - x2) / (y1 - y2);
   

    mx2 = (x2 + x3) / 2;
    my2 = (y2 + y3) / 2;
    if(y2 - y3 == 0) M2 = 0;
    else  M2 = (-1)*(x2 - x3) / (y2 -y3);
    

    if(M1 == M2){
      px = mx1;
      py = my2;
    }
    else if(M1 != M2){
      px = (M1*mx1 - my1 - M2*mx2 + my2) / (M1 - M2);
      py = M1*(px - mx1) + my1;
    }

    r = sqrt((x1 - px)*(x1 - px) + (y1 - py)*(y1 - py));

    printf("%.3f %.3f %.3f\n",px,py,r);
    n--;
  }
 return 0; 
}