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++: #define _USE_MATH_DEFINES

#include <cstdio>
#include <cstdlib>
#include <iostream>
#include <cmath>
#include <algorithm>
#include <vector>
#include <queue>
#include <map>

using namespace std;

typedef pair<long long int, long long int> P;
long long int INF = 1e18;

double round_(double d){
	double ret = (int)(abs(d) * 1000 * 2 + 1) / 2 / 1000.0;
	ret *= d / abs(d);
	return ret;
}

int main()
{
    const double EPS = 1.0e-10;
    double a,b,c,d,e,f;
    double x1,x2,x3,y1,y2,y3;
    double x,y,r;
    int n;
	cin >> n;
    for(int i = 0; i < n; i++){
    	cin >> x1 >> y1 >> x2 >> y2 >> x3 >> y3;
        a = x1 - x2;
        b = y1 - y2;
        c = (x1 * x1 + y1 * y1 - x2 * x2 - y2 * y2) / 2;
        d = x1 - x3;
        e = y1 - y3;
        f = (x1 * x1 + y1 * y1 - x3 * x3 - y3 * y3) / 2;
        x = (e * c - b * f) / (a * e - b * d);
        y = (a * f - d * c) / (a * e - b * d);
    	r = sqrt((x1 - x) * (x1 - x) + (y1 - y) * (y1 - y));
    	x = round_(x);
    	y = round_(y);
    	r = round_(r);
//        if(-0.0005 < x && x < 0.0+EPS) x = 0.0;
//        if(-0.0005 < y && y < 0.0+EPS) y = 0.0;
 
        printf("%.3f %.3f %.3f\n",x,y,r);
    }
    return 0;
}

C++: #include <iostream>
#include <cstdio>
#include <stdio.h>
#include <math.h>
using namespace std;
int main(){
	int n;
	cin>>n;
	for(int i=0;i<n;i++){
		double x1,y1,x2,y2,x3,y3,xp,yp,r;
		cin>>x1>>y1>>x2>>y2>>x3>>y3;
		double a=x2-x1,b=y2-y1,c=x3-x1,d=y3-y1;
		if(a==0){
			xp = c/2+d/2/c-b*d/2/c;
			yp = b/2;
		}else if(b==0){
			xp = a/2;
			yp = -a*c/2/d+c*c/2/d+d/2;
		}else if(c==0){
			xp = a/2+b/2/a-d*b/2/a;
			yp = d/2;
		}else if(d==0){
			xp = c/2;
			yp = -a*c/2/b+a*a/2/b+b/2;
		}else{
			xp = (d*(a*a+b*b)-b*(c*c+d*d))/(a*d-b*c)/2;
			yp = -a*xp/b+a*a/2/b+b/2;
		}
		r = sqrt((x1-xp)*(x1-xp)+(y1-yp)*(y1-yp));
		printf("%.3lf %.3lf %.3lf\n",xp,yp,r);
	}
	return 0;
}

C++: #include<bits/stdc++.h>
using namespace std;
 
#define REP(i,s,n) for(int i=s;i<n;++i)
#define rep(i,n) REP(i,0,n)
#define SORT(c) sort((c).begin(),(c).end())
#define IINF INT_MAX
#define LLINF LLONG_MAX
 
typedef long long ll;
typedef pair<int, int> ii;
 
int main(){

	int n;
	cin >> n;
	rep(i, n){
		double x1, y1, x2, y2, x3, y3;
		cin >> x1 >> y1 >> x2 >> y2 >> x3 >> y3;
		double vx21, vx31, vy21, vy31, tmp1, tmp2;
		vx21 = 2 * (x1 - x2);
		vx31 = 2 * (x1 - x3);
		vy21 = 2 * (y1 - y2);
		vy31 = 2 * (y1 - y3);
		tmp1 = x1 * x1 + y1 * y1 - x2 * x2 - y2 * y2;
		tmp2 = x1 * x1 + y1 * y1 - x3 * x3 - y3 * y3;
		
		double x, y, r;
		x = -(vy21 * tmp2 - vy31 * tmp1) / (vy31 * vx21 - vy21 * vx31);
		y = -(vx21 * tmp2 - vx31 * tmp1) / (vx31 * vy21 - vx21 * vy31);
		r = sqrt((x1 - x) * (x1 - x) + (y1 - y) * (y1 - y));
		
		printf("%.3lf %.3lf %.3lf\n", x, y, r);
		
	}
 
	return 0;
}

C++: #include<cstdio>
#include<cmath>

//#include<iostream>
using namespace std;

int main(){
	int n;
	float x1, y1, x2, y2, x3, y3, xp,yp, xq, yq, s1, sr1, s2, sr2;
	float b1, b2, xc, yc, r;
	scanf("%d", &n);
	while(n--){
		scanf("%f%f%f%f%f%f",&x1, &y1, &x2, &y2, &x3, &y3);

		if(!(y2-y1)){ 
			r=x1; x1=x3; x3=r; r=y1; y1=y3; y3=r;
		}
		xp=(x2+x1)/2; yp=(y2+y1)/2;
		xq=(x3+x1)/2; yq=(y3+y1)/2;
		sr1=-(x2-x1)/(y2-y1); b1=yp-sr1*xp;
		sr2=-(x3-x1)/(y3-y1); b2=yq-sr2*xq;

		xc=-(b1-b2)/(sr1-sr2);
		yc=sr1*xc+b1;
		r=sqrt((xc-x1)*(xc-x1)+(yc-y1)*(yc-y1));
		printf("%.3f %.3f %.3f\n",xc, yc, r);
	}
	return 0;
}

C++: #include <cmath>
#include <cstdio>
using namespace std;
int main()
{
	int n;
	double x, y, x1, x2, x3, y1, y2, y3, a1, a2, b1, b2, c1, c2;
	scanf("%d", &n);
	for( ; n > 0; n--) {
		scanf("%lf%lf%lf%lf%lf%lf", &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);
		printf("%.3lf %.3lf %.3lf\n", x, y, hypot(x - x1, y - y1));
	}

	return 0;
}