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 x[4],y[4];
    int n;
    scanf("%d",&n);
    for(int i=0;i<n;i++){
        for(int i=0;i<3;i++)scanf("%lf%lf",&x[i],&y[i]);
        x[3]=y[0]*(x[2]*x[2]+y[2]*y[2])+y[1]*(x[0]*x[0]+y[0]*y[0])+y[2]*(x[1]*x[1]+y[1]*y[1])-y[0]*(x[1]*x[1]+y[1]*y[1])-y[1]*(x[2]*x[2]+y[2]*y[2])-y[2]*(x[0]*x[0]+y[0]*y[0]);
        y[3]=x[0]*(x[2]*x[2]+y[2]*y[2])+x[1]*(x[0]*x[0]+y[0]*y[0])+x[2]*(x[1]*x[1]+y[1]*y[1])-x[0]*(x[1]*x[1]+y[1]*y[1])-x[1]*(x[2]*x[2]+y[2]*y[2])-x[2]*(x[0]*x[0]+y[0]*y[0]);
        y[3]=-y[3];
        x[3]/=x[0]*y[1]+x[1]*y[2]+x[2]*y[0]-x[0]*y[2]-x[1]*y[0]-x[2]*y[1];
        y[3]/=x[0]*y[1]+x[1]*y[2]+x[2]*y[0]-x[0]*y[2]-x[1]*y[0]-x[2]*y[1];
        y[3]/=2;
        x[3]/=2;
        printf("%.3f %.3f %.3f\n",x[3]-0.0005,y[3]-0.0005,sqrt((x[3]-x[0])*(x[3]-x[0])+(y[3]-y[0])*(y[3]-y[0]))-0.0005);
    }
}

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

using namespace std;

int main(){

	double x[3+1],y[3+1];
	double xp,yp;
	double a[2+1],b[2+1],c[2+1];
	double r;
	for(int i=1;i<4;i++){
		cin>>x[i];
		cin>>y[i];
	}

	a[1]=2*(x[2]-x[1]);
	b[1]=2*(y[2]-y[1]);
	c[1]=x[1]*x[1]-x[2]*x[2]+y[1]*y[1]-y[2]*y[2];
	a[2]=2*(x[3]-x[1]);
	b[2]=2*(y[3]-y[1]);
	c[2]=x[1]*x[1]-x[3]*x[3]+y[1]*y[1]-y[3]*y[3];

	xp=(b[1]*c[2]-b[2]*c[1])/(a[1]*b[2]-a[2]*b[1]);
	yp=(c[1]*a[2]-c[2]*a[1])/(a[1]*b[2]-a[2]*b[1]);

	r=sqrt( (xp-x[1]*xp-x[1])+(yp-y[1])*(yp-y[1])  );

	printf("%.3f %.3f %.3f",xp,yp,r);

	return 0;

}

C++: #include<iostream>
#include<iomanip>
#include<cmath>
#define PI 3.1415
using namespace std;

int main(){

	int n;
	double x1, y1, x2, y2, x3, y3;
	double la, lb, lc;
	double a, b, c;
	
	double r;
	double px, py;

	cin >> n;

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

		//lc = (x1 - x2) * (x1 - x2) + (y1 - y2) * (y1 - y2);
		la = (x2 - x3) * (x2 - x3) + (y2 - y3) * (y2 - y3);
		//lb = (x3 - x1) * (x3 - x1) + (y3 - y1) * (y3 - y1);

		a = fabs((atan2( y2 - y1, x2 - x1 ) - atan2( y3 - y1, x3 - x1 )));
		b = fabs((atan2( y1 - y2, x1 - x2 ) - atan2( y3 - y2, x3 - x2 )));
		c = fabs((atan2( y1 - y3, x1 - x3 ) - atan2( y2 - y3, x2 - x3 )));


		if( a >= PI ) a=2*PI-a;
		if( b >= PI ) b=2*PI-b;
		if( c >= PI ) c=2*PI-c;


		r = sqrt(la) / (sin(a)*2);
		px = ( sin(2*a) * x1 + sin(2*b) * x2 + sin(2*c) * x3 ) / (sin(2*a)+sin(2*b)+sin(2*c));
		py = ( sin(2*a) * y1 + sin(2*b) * y2 + sin(2*c) * y3 ) / (sin(2*a)+sin(2*b)+sin(2*c));

		r = floor(r*1000+0.5)/1000;
		px = floor(px*1000+0.5)/1000;
		py = floor(py*1000+0.5)/1000;

		cout << setprecision(3) << fixed  << px << " " << py << " " << r << endl;

	}
	return 0;
}

C++: #include<iostream>
#include<cstdio>
#include<cmath>
using namespace std;
int main(){
  int n;
  cin >>n;
  while(n--){
    double p[3][2];
    for(int i=0; i<3; i++)
      for(int j=0; j<2; j++)
	cin >>p[i][j];
    for(int i=1; i<3; i++)
      for(int j=0; j<2; j++)
	p[i][j]-=p[0][j];
    double m[2][2],det,im[2][2],x[2],s[2];
    for(int i=0; i<2; i++)
      for(int j=0; j<2; j++)
	m[i][j] = 2*p[i+1][j];
    for(int  i=0; i<2; i++)
      x[i] = p[i+1][0]*p[i+1][0]+p[i+1][1]*p[i+1][1];
    det = m[0][0]*m[1][1]-m[0][1]*m[1][0];
    im[0][0] = m[1][1]/det;
    im[0][1] = -m[0][1]/det;
    im[1][0] = -m[1][0]/det;
    im[1][1] = m[0][0]/det;
    for(int i=0; i<2; i++)
      s[i] = im[i][0]*x[0]+im[i][1]*x[1];
    printf("%.3lf %.3lf %.3lf\n",s[0]+p[0][0],s[1]+p[0][1],sqrt(s[0]*s[0]+s[1]*s[1]));
  }
  return 0;
}