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 <complex>
#include <cmath>
using namespace std;

typedef complex<double> point;

#define PI M_PI
#define EPS (1e-10)
#define X real()
#define Y imag()

class Triangle{
private:	
	point a,b,c;
	double edgeA,edgeB,edgeC;
	double angleA,angleB,angleC;
	double calc_angle(double a,double b, double c){
		return acos((b*b+c*c-a*a)/(2.0*b*c));
	}
	bool equal(double a, double b){
		return (abs(a-b) < EPS)? true: false;
	}

public:
	Triangle(point p1,point p2,point p3){
		a=p1; b=p2; c=p3;
		edgeA=abs(b-c);
		edgeB=abs(c-a);
		edgeC=abs(a-b);
		angleA=calc_angle(edgeA,edgeB,edgeC);
		angleB=calc_angle(edgeB,edgeC,edgeA);
		angleC=calc_angle(edgeC,edgeA,edgeB);
	}
	double circumscribed_radius(){
		return (edgeA/(2.0*sin(angleA)));
	}
	double circumscribed_X(){
		double A=sin(2.0*angleA);
		double B=sin(2.0*angleB);
		double C=sin(2.0*angleC);
		return((a.X*A+b.X*B+c.X*C)/(A+B+C));
	}
	double circumscribed_Y(){
		double A=sin(2.0*angleA);
		double B=sin(2.0*angleB);
		double C=sin(2.0*angleC);
		return((a.Y*A+b.Y*B+c.Y*C)/(A+B+C));
	}
};

int main(void){
	double x1,y1;
	double x2,y2;
	double x3,y3;
	int n;
	double r,px,py;

	cin >> n;
	for(int i=0;i<n;i++){
		cin >> x1 >> y1 >> x2 >> y2 >> x3 >> y3;
		point p1(x1,y1);
		point p2(x2,y2);
		point p3(x3,y3);
		Triangle Tr(p1,p2,p3);
		r=Tr.circumscribed_radius();
		px=Tr.circumscribed_X();
		py=Tr.circumscribed_Y();
		cout << fixed;
		cout.precision(3);
		cout << px << " " << py << " " << r << endl;
		if(i==20) break;
	}
	return 0;
}

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

using namespace std;

int n;
double x[3], y[3];

int main()
{
	cin >> n;
	for(int i=0; i<n; i++)
	{
		cin >> x[0] >> y[0] >> x[1] >> y[1] >> x[2] >> y[2];
		double a1 = 2.0 * (x[1] - x[0]);
		double b1 = 2.0 * (y[1] - y[0]);
		double c1 = x[0]*x[0] - x[1]*x[1] + y[0]*y[0] - y[1]*y[1];
		double a2 = 2.0 * (x[2] - x[0]);
		double b2 = 2.0 * (y[2] - y[0]);
		double c2 = x[0]*x[0] - x[2]*x[2] + y[0]*y[0] - y[2]*y[2];

		double cx = (b1*c2-b2*c1) / (a1*b2-a2*b1);
		double cy = (c1*a2-c2*a1) / (a1*b2-a2*b1);
		
		double dx = x[0] - cx;
		double dy = y[0] - cy;
		double r = sqrt(dx*dx + dy*dy);
		
		printf("%.3f %.3f %.3f\n", cx, cy, r);
	}
}

C++: #include <stdio.h>
#include <math.h>
 
int main()
{
    int i, n;
    double x1, x2, x3, y1, y2, y3;
    double a, b, c, d, e, f;
    double X1, Y1, r;
     
    scanf("%d", &n);
    for (i = 0; i < n; i++){
        scanf("%lf %lf %lf %lf %lf %lf",&x1, &y1, &x2, &y2, &x3, &y3);
        a = 2 * (x2 - x1);
        b = 2 * (y2 - y1);
        c = x1*x1 - x2*x2 + y1*y1 - y2*y2;
        d = 2 * (x3 - x1);
        e = 2 * (y3 - y1);
        f = x1*x1 - x3*x3 + y1*y1 - y3*y3;
         
        X1 = (b*f - e*c) / (a*e - d*b);
        Y1 = (c*d - f*a) / (a*e - d*b);
        r  = sqrt((X1-x1)*(X1-x1) + (Y1-y1)*(Y1-y1));
         
        // X1 *= 1000;
        // Y1 *= 1000;
        // r  *= 1000;
         
        // X1 = (int)(X1 > 0.0 ? X1+0.5 : X1-0.5);
        // Y1 = (int)(Y1 > 0.0 ? Y1+0.5 : Y1-0.5);
        // r  = (int)(r  > 0.0 ? r +0.5 : r -0.5);
         
        // X1 = (double)X1/1000;
        // Y1 = (double)Y1/1000;
        // r  = (double)r /1000;
         
        printf("%.3f %.3f %.3f\n", X1, Y1, r);
         
         
    }
     
    return 0;
}

C++: 
#include <iostream>
#include <cstdlib>
#include <cstdio>
#include <cmath>
#include <stack>
#include <cctype>
#include <complex>
#include <vector>
#include <algorithm>

using namespace std;


bool solve(){
	complex<double> Ans;
	complex<double> P[3];
	for(int i=0;i<3;i++){
		cin>> P[i].real()>> P[i].imag();
	}
	complex<double> T[2];
	complex<double> K[2];
	double katamuki[2];
	for(int i=0;i<2;i++){
		T[i].real() = (P[i].real() + P[i+1].real()) / 2;
		T[i].imag() = (P[i].imag() + P[i+1].imag()) / 2;
		complex<double> N;
		N = (P[i+1]-P[i])/abs(P[i+1]-P[i]);
		K[i].real() =  N.imag();
		K[i].imag() = -N.real();
	}
	int a = (T[1]-T[0]).real();
	int b = (T[1]-T[0]).imag();
	int x0 = K[0].real();
	int y0 = K[0].imag();
	int x1 = K[1].real();
	int y1 = K[1].imag();
	int m = ( a * y0 - b * x0 ) / ( x0 * y1 - x1 * y0);
	K[1] *= m;
	Ans = K[1] + T[1];


	printf("%.3f %.3f %.3f", Ans.real(), Ans.imag(), abs(Ans-P[0]));
	printf("\n");
	
	return true;
}

int main(){
	cout.setf(ios::fixed);
	cout.precision(5);
	int n;
	cin>> n;
	for(int i=0;i<n;i++){
		solve();
	}
	return 0;
}