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

#define EPS 1e-9

double get_angle( double x1, double y1, double x2, double y2 )
{
	double angle;
	double m;
	if ( x1 == x2 ) angle = 90.0;
	else
	{
		m = ( y2 - y1 ) / ( x2 - x1 );
		angle = atan( m ) * 180.0 / M_PI;
	}
	return angle;
}

double get_radian( double x1, double y1, double x2, double y2 )
{
	if ( x1 == x2 ) return M_PI / 180.0;
	return atan( ( y2 - y1 ) / ( x2 - x1 ) );
}

double get_distance( double x1, double y1, double x2, double y2 )
{
	return sqrt( ( x2 - x1 ) * ( x2 - x1 ) + ( y2 - y1 ) * ( y2 - y1 ) );
}

int main( void )
{
	int n; cin >> n;
	
	double x1, y1, x2, y2, x3, y3;
	for ( int i = 0; i < n; i++ )
	{
		cin >> x1 >> y1 >> x2 >> y2 >> x3 >> y3;

		double x12 = ( x1 + x2 ) / 2.0;
		double y12 = ( y1 + y2 ) / 2.0;
		double a12 = get_angle( x1, y1, x2, y2 ) - 90.0;
		double x13 = ( x1 + x3 ) / 2.0;
		double y13 = ( y1 + y3 ) / 2.0;
		double a13 = get_angle( x1, y1, x3, y3 ) - 90.0;

		double t12 = tan( a12 * M_PI / 180.0 );
		double t13 = tan( a13 * M_PI / 180.0 );
		double x, y;
		if ( fabs( a12 - 90.0 ) <= EPS || fabs( a12 + 90.0 ) <= EPS )
		{
			y = t13 * ( x12 - x13 ) + y13;
			x = x12;
		}
		else if ( fabs( a13 - 90.0 ) <= EPS || fabs( a13 + 90.0 ) <= EPS )
		{
			y = t12 * ( x13 - x12 ) + y12;
			x = x13;
		}
		else
		{
			x = ( t12 * x12 - t13 * x13 + y13 - y12 ) / ( t12 - t13 );
			y = t12 * ( x - x12 ) + y12;
		}
		double r = get_distance( x1, y1, x, y );

		/*
		cout << "=== test ==============" << endl;
		cout << "a12 = " << a12 << endl;
		cout << "t12 = " << t12 << endl;
		cout << "x12 = " << x12 << endl;
		cout << "y12 = " << y12 << endl;
		cout << endl;
		cout << "a13 = " << a13 << endl;
		cout << "t13 = " << t13 << endl;
		cout << "x13 = " << x13 << endl;
		cout << "y13 = " << y13 << endl;
		cout << "=======================" << endl;
		*/

		cout.setf( ios::fixed );
		cout.precision( 3 );
		cout << x << " " << y << " " << r << endl;
	}

	return 0;
}

C++: #include <bits/stdc++.h>
using namespace std;


int main() {
    int T;
    cin >> T;
    double e,f,a,b,c,d;
    while(T--) {
        cin >> e >> f >> a >> b >> c >> d;
        a -= e; c -= e;
        b -= f; d -= f;
        double den = 2 * (d * a - b * c);
        double y = a * (c * c + d * d) - c * (a * a + b * b);
        double x = b * (c * c + d * d) - d * (a * a + b * b);
        y /= den;
        x /= -den;
        printf("%.3lf %.3lf %.3lf\n", x + e, y + f, sqrt(x * x + y * y));
    }
}

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

using namespace std;

int main() {
	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;
		double veku1[3], veku2[3];
		veku1[0] = x2-x1;
		veku1[1] = y2-y1;
		veku2[0] = x3-x1;
		veku2[1] = y3-y1;
		veku1[2] = veku1[0]*veku1[0]+veku1[1]*veku1[1];
		veku2[2] = veku2[0]*veku2[0]+veku2[1]*veku2[1];
		double naiseki = veku1[0]*veku2[0]+veku1[1]*veku2[1];
		double p, q;
		q = (veku1[2]*veku2[2]-naiseki*veku1[2])/(2.0*(veku1[2]*veku2[2]-naiseki*naiseki));
		p = (veku1[2]*veku2[2]-naiseki*veku2[2])/(2.0*(veku1[2]*veku2[2]-naiseki*naiseki));
		double k[2];
		k[0] = x1+p*veku1[0]+q*veku2[0];
		k[1] = y1+p*veku1[1]+q*veku2[1];
		double pp = sqrt((k[0]-x1)*(k[0]-x1)+(k[1]-y1)*(k[1]-y1));
		k[0] *= 1000.0;
		if (k[0]-(int)k[0] >= 0.5) {
			k[0] += 1.0;
		}
		k[0] /= 1000.0;
		k[1] *= 1000.0;
		if (k[1]-(int)k[1] >= 0.5) {
			k[1] += 1.0;
		}
		k[1] /= 1000.0;
		pp *= 1000.0;
		if (pp-(int)pp >= 0.5) {
			pp += 1.0;
		}
		pp /= 1000.0;
		printf("%.3f %.3f %.3f\n", k[0], k[1], pp);
	}
	return 0;
}