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<stdio.h>
#include<iostream>
#include<math.h>

struct Zahyou
{
	float x, y;
};

int main()
{
	int n;
	Zahyou de[4];

	scanf("%d", &n);
	for (int i = 0; i < n; i++)
	{
		for (int j = 1; j < 4; j++)
		{
			scanf("%f %f", &de[j].x, &de[j].y);
		}
		de[0].x = ((de[1].y - de[3].y)*(pow(de[1].y, 2) - pow(de[2].y, 2) + pow(de[1].x, 2) - pow(de[2].x, 2)) + (de[1].y - de[2].y)*(pow(de[1].y, 2) - pow(de[3].y, 2) + pow(de[1].x, 2) - pow(de[3].x, 2))) / (2 * (de[1].y - de[3].y)*(de[1].x - de[2].x) + 2 * (de[1].y - de[2].y)*(de[1].x - de[3].x));
		de[0].y = ((de[1].x - de[3].x)*(pow(de[1].x, 2) - pow(de[2].x, 2) + pow(de[1].y, 2) - pow(de[2].y, 2)) + (de[1].x - de[2].y)*(pow(de[1].x, 2) - pow(de[3].x, 2) + pow(de[1].y, 2) - pow(de[3].y, 2))) / (2 * (de[1].x - de[3].x)*(de[1].y - de[2].y) + 2 * (de[1].x - de[2].x)*(de[1].y - de[3].y));
		
		printf("%.3f %.3f %.3f\n",de[0].x,de[0].y,sqrt(pow((de[0].x-de[1].x),2)+pow((de[0].y-de[1].y),2)));
	}
	return 0;
}

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

int main(){
    int n;
    double x1, x2, x3, y1, y2, y3, x, y;
    cin >> n;
    for(int i = 0;i < n;i++){
	cin >> x1 >> y1 >> x2 >> y2 >> x3 >> y3;
	if(y1 == y2)swap(x1, x3), swap(y1, y3);
	else if(y1 == y3)swap(x1, x2), swap(y1, y2);
	double x = (x3-x1)/(y1-y3)*(x1+x3)/2-(x2-x1)/(y1-y2)*(x1+x2)/2+(y1+y2)/2-(y1+y3)/2;
	x /= ((x3-x1)/(y1-y3) - (x2-x1)/(y1-y2));
	double y = (x2-x1)/(y1-y2)*(x - x1+x2/2) + (y1+y2)/2;
	cout << x << " " << y << " " << hypot(x1-x,y1-y) << endl;   
    }
    return 0;
}

C++: #include <iostream>
#include <iomanip>
#include <algorithm>
#include <math.h>
using namespace std;
int main( void )
{
	int n;
	cin >> n;
	for ( int i = 0; i < n; i++ )
	{
		double x1, y1, x2, y2, x3, y3;
		cin >> x1 >> y1 >> x2 >> y2 >> x3 >> y3;

		for ( int j = 0; j < 3; j++ )
		{
			swap( x1, x2 );
			swap( y1, y2 );
			swap( x2, x3 );
			swap( y2, y3 );

			double a = 2.0 * x1 - 2.0 * x2;
			double b = 2.0 * y1 - 2.0 * y2;
			double c = 2.0 * x2 - 2.0 * x3;
			double d = 2.0 * y2 - 2.0 * y3;

			if ( a * b - c * d == 0.0 )
				continue;

			double e = x1 * x1 - x2 * x2 + y1 * y1 + y2 * y2;
			double f = x2 * x2 - x3 * x3 + y2 * y2 + y3 * y3;

			double x0 = ( d * e - b * f ) / ( a * b - c * d );
			double y0 = ( a * f - c * e ) / ( a * b - c * d );

			if ( x0 == -0.0 )
				x0 = 0.0;
			if ( y0 == -0.0 )
				y0 = 0.0;

			double r1 = sqrt( (x1-x0)*(x1-x0) + (y1-y0)*(y1-y0) );
			double r2 = sqrt( (x2-x0)*(x2-x0) + (y2-y0)*(y2-y0) );
			double r3 = sqrt( (x3-x0)*(x3-x0) + (y3-y0)*(y3-y0) );

			cout.setf( ios::fixed, ios::floatfield );
			cout << setprecision(3);
			if ( r1 == r2 && r1 == r3 )
				cout << x0 << " " << y0 << " " << r1 << endl;
		}

	}
	return 0;
}

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

using namespace std;

int main() {
	double x[3], y[3];
	double a, b, c;
	double A[2], B[2], C[2];
	double px, py;
	double r;
	int n;
	cin >> n;
	for (int i = 0; i < n; i++) {
		cin >> x[0] >> y[0] >> x[1] >> y[1] >> x[2] >> y[2];
		A[0] = 2 * (x[1] - x[0]);
		B[0] = 2 * (y[1] - y[0]);
		C[0] = pow(x[0], 2) - pow(x[1], 2) + pow(y[0], 2) - pow(y[1], 2);
		A[1] = 2 * (x[2] - x[0]);
		B[1] = 2 * (y[2] - y[0]);
		C[1] = pow(x[0], 2) - pow(x[2], 2) + pow(y[0], 2) - pow(y[2], 2);
		px = ((B[0] * C[1]) - (B[1] * C[0])) / ((A[0] * B[1]) - (A[1] * B[0]));
		py = ((C[0] * A[1]) - (C[1] * A[0])) / ((A[0] * B[1]) - (A[1] * B[0]));
		a = sqrt(pow(x[1] - x[0], 2) + pow(y[1] - y[0], 2));
		b = sqrt(pow(x[2] - x[0], 2) + pow(y[2] - y[0], 2));
		c = sqrt(pow(x[2] - x[1], 2) + pow(y[2] - y[1], 2));
		r = (a * b * c) / sqrt((a+b+c) * (-a+b+c) * (a-b+c) * (a+b-c));
		printf("%.3lf %.3lf %.3lf\n", px, py, r);
	}
	return 0;
}