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<cmath>
#include<cstdio>
#define S second
#define F first
using namespace std;
typedef pair<double,double> P;

double Length(P p,P q){
  return sqrt(pow(p.first - q.first,2)+pow(p.second-q.second,2));
}

int main(){
  P p[3];
  double a,b,c,A,B,C,R,x,y;
  int n;
  cin >> n;
  while(n-- > 0){ 
    cin >> p[0].first >> p[0].second >> p[1].first >>p[1].second >> p[2].first >> p[2].second;
    a = Length(p[0],p[1]);
    b = Length(p[1],p[2]);
    c = Length(p[2],p[0]);
    A = acos((b*b+c*c-a*a)/(2*b*c));
    B = acos((a*a+c*c-b*b)/(2*a*c));
    C = acos((a*a+b*b-c*c)/(2*a*b));
    R = 0.5 * (a/sin(A));
    //x = 0.5*((((pow(p[0].F,2)+pow(p[0].S,2))*(p[1].S-p[2].S)+((pow(p[1].F,2)+pow(p[1].F,2))*(p[2].S-p[0].S))+((pow(p[2].F,2)+pow(p[2].S,2))*(p[0].S-p[1].S))) )   / (p[0].F*(p[1].S-p[2].S)+p[1].F*(p[2].S-p[0].S)+p[2].F*(p[0].S-p[1].S)));
    x = 0.5*( (pow(p[0].F,2)+pow(p[0].S,2))*(p[1].S-p[2].S) + (pow(p[1].F,2)+pow(p[1].S,2))*(p[2].S-p[0].S) + (pow(p[2].F,2)+pow(p[2].S,2))*(p[0].S-p[1].S)                           )/(       
																							 p[0].F*(p[1].S-p[2].S) + p[1].F*(p[2].S-p[0].S) + p[2].F*(p[0].S-p[1].S)            );

    y = 0.5*((pow(p[0].F,2)+pow(p[0].S,2))*(p[1].F-p[2].F)+(pow(p[1].F,2)+pow(p[1].S,2))*(p[2].F-p[0].F)+(pow(p[2].F,2)+pow(p[2].S,2))*(p[0].F-p[1].F))/(p[0].S*(p[1].F-p[2].F)+p[1].S*(p[2].F-p[0].F)+p[2].S*(p[0].F-p[1].F));

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

C++: #include<iostream>
#include<string>
#include<cstdio>
#include<cstring>
#include<algorithm>
#include<cmath>
using namespace std;
int main(void){

    double A1,A2,B1,B2,C1,C2,X1,X2,X3,Y1,Y2,Y3,X,Y,r;
    int n;
    cin>>n;
    for(int i=0;i<n;i++){
    cin>>X1>>X2>>X3>>Y1>>Y2>>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);
    X+=0.0005,Y+=0.0005;
    X=floor(X),Y=floor(Y);

    r=sqrt((X1-X)*(X1-X)+(Y2-Y)*(Y2-Y));

    printf("%.3lf %.3lf %.3lf",X,Y,r);
    }

	return 0;
}

C++: #include <iostream>

#include <cmath>



using namespace std;



int main(){

	int n;

	double r,a,b,x[3],y[3];

	while(n){

	cin >> x[1] >> y[1] >> x[2] >> y[2] >> x[3] >> y[3];

	/*ツづ慊つクツづ債青板値ツづ個計ツ算*/

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

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

	r=sqrt((x[1]-a)*(x[1]-a)+(y[1]-b)*(y[1]-b));

	printf("%.3f %.3f %.3f\n",a,b,r);

	}

}

C++: #include <cstdio>
#include <cstdlib>
#include <iostream>
#include <algorithm>
#include <cstring>
#include <string.h>
#include <bitset>
#include <queue>
#include <map>
#include <string>
#include <stack>
#include <utility>
#include <queue>
#include <cmath>
#define mp make_pair
#define pii pair<long long int,long long int> 
#define ff first
#define pb push_back
#define ss second
#define ll long long 
#define ull unsigned long long
#define vi vector<long long int>
#define vii vector<pii>
#define vvi vector <vi>
#define rep(x,a,b,c) for(int x=a;x<=b;x+=c)
#define repp(x,a,b) rep(x,a,b,1)
#define rev(x,a,b,c) for(int x=a;x>=b;x-=c)
#define revv(x,a,b) rev(x,a,b,1)
#define OO (int)2e9
#define INF (ll)1e18
 
using namespace std;

double a,b,c,d,xx,yy,x2,y2,x3,y3;
int tc;

double xc()
{
	return ((xx*xx+yy*yy)*(y2-y3)+(x2*x2+y2*y2)*(y3-yy)+(x3*x3+y3*y3)*(yy-y2))/(double)d;
}

double yc()
{
	return ((xx*xx+yy*yy)*(x3-x2)+(x2*x2+y2*y2)*(xx-x3)+(x3*x3+y3*y3)*(x2-xx))/(double)d;
}

double rads()
{
	return sqrt(abs(xx-xc())*abs(xx-xc())+abs(yy-yc())*abs(yy-yc()));
}

double findabc()
{
	a=sqrt((abs(x2-xx))*(abs(x2-xx))+(abs(y2-yy))*(abs(y2-yy)));
	b=sqrt((abs(x3-x2))*(abs(x3-x2))+(abs(y3-y2))*(abs(y3-y2)));
	c=sqrt((abs(x3-xx))*(abs(x3-xx))+(abs(y3-yy))*(abs(y3-yy)));
	d=2*(xx*(y2-y3)+x2*(y3-yy)+x3*(yy-y2));
}

int main()
{
	scanf("%d",&tc);
	while(tc--)
	{
		scanf("%lf %lf %lf %lf %lf %lf",&xx,&yy,&x2,&y2,&x3,&y3);
		findabc();
		//printf("%.3lf %.3lf %.3lf",a,b,c);
		printf("%.3lf %.3lf %.3lf\n",xc(),yc(),rads());
	}
	return 0;
}