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 <cstdio>
#include <cctype>
#include <iostream>
#include <sstream>
#include <string>
#include <vector>
#include <map>
#include <stack>
#include <queue>
#include <algorithm>
#include <functional>
#include <complex>
using namespace std;

typedef pair<int, int> pii;
typedef long long ll;
typedef vector<int> vi;
typedef vector<vi> vvi;
typedef vector<string> vs;
typedef complex<double> P;
const double PI = 3.141592653589793238462643383279502884L;
const int LARGE_PRIME = 1000000007;

#define all(c) (c).begin(), (c).end()
#define rall(c) (c).rbegin(), (c).rend()
#define tr(c, i) for(auto i = (c).begin(); i != (c).end(); i++)
#define rtr(c, i) for(auto i = (c).rbegin(); i != (c).rend(); i++)
#define repfn(i,a,cont,next) \
  for(auto i = (a); [=](){return(cont);}(); i = [=](){return(next);}())
#define repby(i,a,b,step) repfn(i, a, i < b, i + step)
#define repab(i,a,b) repby(i, (a), (b), 1)
#define rep(i,n) repab(i, 0, (n))
#define pb push_back
#define sz(c) int((c).size())

int main(int argc, char **argv)
{
  int n;
  double x, y;
  cin >> n;

  while (n--) {
    cin >> x >> y;
    P p(x, y);
    cin >> x >> y;
    P q(x, y);
    cin >> x >> y;
    P r(x, y);

    double eA = norm(q - r);
    double eB = norm(r - p);
    double eC = norm(p - q);

    P c = (eA*(eB+eC-eA)*p + eB*(eC+eA-eB)*q + eC*(eA+eB-eC)*r)
          / (eA*(eB+eC-eA) + eB*(eC+eA-eB) + eC*(eA+eB-eC));

    printf("%.3f %.3f %.3f\n", c.real(), c.imag(), abs(p - c));

  }
  return 0;
}

C++: #include <cstdio>
#include <cstring>
#include <cmath>
#include <vector>
#include <map>
#include <algorithm>
#include <iostream>
#include <iomanip>

#define rep(i, j) FOR(i, 0, j)
#define FOR(i, j, k) for(int i = j; i < k; ++i)
#define SQ(i) ((i) * (i))
using namespace std;

int main(){
  double x1, y1, x2, y2, x3, y3;
  double a1, b1, c1, a2, b2, c2, x, y, a, b, c, cos_a, sin_a, r;
  int n;
  scanf("%d", &n);
  while(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 * c1 - b2 * c1) / (a1 * b2 - a2 * b1);
    y = (c1 * a2 - c2 * a1) / (a1 * b2 - a2 * b1);

    r = SQ(x3-x) + SQ(y3 - y);
    r = sqrt(r);
    printf("%.3f %.3f %.3f\n",x, y, r);
  }
  return 0;
}

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

using namespace std;

int main(void){
	int n;
	double x1,y1,x2,y2,x3,y3,m1,m2,x,y,r;
	double xa,ya,xb,yb,xc,yc;
	cin>>n;
	for(int i=0;i<n;i++){
		cin>>xa>>ya>>xb>>yb>>xc>>yc;
		if(yb==ya){
			x1=xb; y1=yb;
			x2=xc; y2=yc;
			x3=xa; y3=ya;
		} else if(yc==yb){
			x1=xb; y1=yb;
			x2=xa; y2=ya;
			x3=xc; y3=yc;
		} else {
			x1=xa; y1=ya;
			x2=xb; y2=yb;
			x3=xc; y3=yc;
		}
		m1=(x2-x1)/(y2-y1);
		m2=(x3-x2)/(y3-y2);
		x=(1/(m2-m1))*(y3-y1)+(x1+x2)/2*m1-(x2+x3)/2*m2;
		y=(x-(x1+x2)/2)*m1+(y1+y2)/2;
		r=sqrt((x1-x)*(x1-x)+(y1-y)*(y1-y));
		printf("%.3f %.3f %.3f\n",x,y,r);
	}
}

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

using namespace std;

struct point{
     double x, y;
};

void renritu(point p1, point p2, double *a, double *b, double *c){
    *a=2*(p2.x-p1.x);
    *b=2*(p2.y-p1.y);
    *c=p1.x*p1.x+p1.y*p1.y-(p2.x*p2.x+p2.y*p2.y);
}

int main(void){
    int i,n;
    double a1,b1,c1,a2,b2,c2,r;
    point p1,p2,p3;
    cin >> n;
    for(i=0;i<n;i++){
        cin >> p1.x >> p1.y >> p2.x >> p2.y >> p3.x >> p3.y;
        renritu(p1,p2,&a1,&b1,&c1);
        renritu(p2,p3,&a2,&b2,&c2);
        p3.x=-(b2-a2)*c1/(a1*b2-a2*b1);
        p3.y=-(a1-b1)*c2/(a1*b2-a2*b1);
        r=sqrt((p3.x-p1.x)*(p3.x-p1.x)+(p3.y-p1.y)*(p3.y-p1.y));
        printf("%.3lf %.3lf %.3lf\n",round(p3.x*1000)/1000,round(p3.y*1000)/1000, round(r*1000)/1000);
    }
    return 0;
}