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<vector>
#include<algorithm>
#include<cmath>
#include<cstdio>

using namespace std;

typedef double Real;

Real EPS = 1e-8;

int sgn(Real a, Real b=0){return a<b-EPS?-1:a>b+EPS?1:0;}
Real sqr(Real a){return sqrt(max(a,(Real)0));}

struct Point{
  Real add(Real a, Real b){
    if(abs(a+b) < EPS*(abs(a)+abs(b)))return 0;
    return a+b;
  }
  Real x, y;
  Point(){}
  Point(Real x,Real y) : x(x) , y(y){}

  Point operator + (Point p){return Point(add(x,p.x), add(y,p.y));}
  Point operator - (Point p){return Point(add(x,-p.x), add(y,-p.y));}
  Point operator * (Real d){return Point(x*d,y*d);}
  Point operator / (Real d){return Point(x/d,y/d);}
  Real norm(){return sqr(x*x+y*y);}
  Real dist(Point a){return (*this-a).norm();}
  Real dot(Point a){return x*a.x+y*a.y;}
  Real cross(Point a){return x*a.y-y*a.x;}
};

struct circle{
  Point p;
  Real r;
  circle(){}
  circle(Point p, Real r) : p(p) , r(r){}
};

circle circumscribedCircle(Point p, Point q, Point r){
  Point a,b,c;
  a=(q-p)*2,b=(r-p)*2;
  c.x=p.dot(p)-q.dot(q);  
  c.y=p.dot(p)-r.dot(r);
  circle res;
  res.p.x=a.y*c.y-b.y*c.x;
  res.p.y=b.x*c.x-a.x*c.y;
  res.p=res.p/a.cross(b);
  return circle(res.p, p.dist(res.p));
}

int main(void){
  int n;
  cin >> n;
  while(n--){
    vector<Point>v(3);
    for(int i=0;i<3;i++)
      cin >> v[i].x >> v[i].y;

    circle res=circumscribedCircle(v[0],v[1],v[2]);
    printf("%.3f %.3f %.3f",res.p.x,res.p.y,res.r);
    cout << endl;
  }
  
  return 0;
}

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

int main()
{
	int n;
	double x1,y1,x2,y2,x3,y3;
	cin >> n;

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

		double a1 = 2*(x2 - x1);
		double b1 = 2*(y2 - y1);
		double c1 = x1*x1 - x2*x2 + y1*y1 - y2*y2;

		double a2 = 2*(x3 -x1);
		double b2 = 2*(y3 - y1);
		double c2 = x1*x1 - x3*x3 + y1*y1 - y3*y3;

		double x = (b1*c2 - b2*c1) / (a1*b2 - a2*b1);
		double y = (c1*a2 - c2*a1) / (a1*b2 - a2*b1);

		double r_2 = (x1 - x)*(x1 - x) + (y1 - y)*(y1 - y);
		double r = sqrt(r_2);

		printf("%.3lf %.3lf %.3lf\n",x,y,r);
	}
	return 0;
}

C++: #include<bits/stdc++.h>
#include<vector>
#include<list>
#include<stack>
#include<queue>
#include<cmath>
#include<algorithm>
using namespace std;

void sol(){
    double x1,y1,x2,y2,x3,y3;
    scanf("%lf %lf %lf %lf %lf %lf",&x1,&y1,&x2,&y2,&x3,&y3);
    double a=sqrt((x1-x2)*(x1-x2)+(y1-y2)*(y1-y2));
    double b=sqrt((x1-x3)*(x1-x3)+(y1-y3)*(y1-y3));
    double c=sqrt((x2-x3)*(x2-x3)+(y2-y3)*(y2-y3));
    double s=(a+b+c)/2;
    double ss=sqrt(s*(s-a)*(s-b)*(s-c));
    double sina=2*ss/b/c;
    double r=a/sina/2;
    a*=a;
    b*=b;
    c*=c;
    double px=(a*(b+c-a)*x3+b*(a+c-b)*x2+c*(a+b-c)*x1)/16/(ss*ss);
    double py=(a*(b+c-a)*y3+b*(a+c-b)*y2+c*(a+b-c)*y1)/16/(ss*ss);
    printf("%.3lf %.3lf %.3lf\n",px,py,r);

}

int main(){
    int n;
    scanf("%d",&n);
    for(int i=0;i<n;i++){
        sol();
    }
    return 0;
}

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

using namespace std;

int sosuu(int n);

int main(){
    double x[3]={0};
    double y[3]={0};
    int i=0;
    scanf("%d",&i);
    while(scanf("%lf",&x[0])!=EOF){
        scanf("%lf",&y[0]);
        scanf("%lf",&x[1]);
        scanf("%lf",&y[1]);
        scanf("%lf",&x[2]);
        scanf("%lf",&y[2]);
        
        double a1= 2*(x[1]-x[0]);
        double b1= 2*(y[1]-y[0]);
        double c1= x[0]*x[0]-x[1]*x[1]+y[0]*y[0]-y[1]*y[1];
        
        double a2= 2*(x[2]-x[0]);
        double b2= 2*(y[2]-y[0]);
        double c2= x[0]*x[0]-x[2]*x[2]+y[0]*y[0]-y[2]*y[2];
        
        double xa = (b1*c2-b2*c1)/(a1*b2-a2*b1);
        double ya = (c1*a2-c2*a1)/(a1*b2-a2*b1);
        
        printf("%.3lf %.3lf",xa,ya);
        
    }
    
}