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>

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

		double const a = sqrt((x2-x1)*(x2-x1) + (y2-y1)*(y2-y1));	
		double const b = sqrt((x3-x2)*(x3-x2) + (y3-y2)*(y3-y2));
		double const c = sqrt((x3-x1)*(x3-x1) + (y3-y1)*(y3-y1));

		double const cosA = (b*b+c*c-a*a)/(2*b*c);
		double const cosB = (a*a+c*c-b*b)/(2*a*c);
		double const cosC = (a*a+b*b-c*c)/(2*a*b);
		double const sinA = sqrt(1-cosA*cosA);

		double const r = a / (sinA * 2);
		//std::cout << "r = " << r << std::endl;

		//std::cout << "cosA = " << cosA << std::endl;
		//std::cout << "cosB = " << cosB << std::endl;
		//std::cout << "cosC = " << cosC << std::endl;

		if(-0.001 < cosA && cosA < 0.001) std::printf("%.3lf %.3lf", (x1+x2) / 2 , (y1+y2) / 2);
		else if (-0.001 < cosB && cosB < 0.001) std::printf("%.3lf %.3lf", (x2+x3) / 2 ,(y2+y3) / 2);
		else if (-0.001 < cosC && cosC < 0.001) std::printf("%.3lf %.3lf", (x1+x3) / 2 , (y1+y3) / 2);
		else
		{
			double const h = sqrt(r*r-(c/2)*(c/2));
				
			//std::cout << "c = " << c << std::endl;
			std::cout << "h = " << h << std::endl;
			
			double const xm = (x1+x3)/2;
			double const ym = (y1+y3)/2;
			std::cout << "xm = " << xm << " ym = " << ym << std::endl;

			double const sinD = (y1-y3) / sqrt((x3-x1)*(x3-x1) + (y3-y1)*(y3-y1));
			double const cosD = (x1-x3) / sqrt((x3-x1)*(x3-x1) + (y3-y1)*(y3-y1));
			std::cout << "sinD = " << sinD << " cosD = " << cosD << std::endl;

			double y4 = h * cosD;
			double x4 = h * sinD;
			std::cout << "x4 = " << x4 << " y4 = " << y4 << std::endl;

			if((sinD < 0 && cosD < 0) || (sinD > 0 && cosD < 0)) x4 *= -1;
			if((sinD == 0 && cosD < 0) || (sinD > 0 && cosD > 0) || (sinD < 0 && cosD > 0)) y4 *= -1;

			double const xd = xm + x4;
			double const yd = ym + y4;


			std::printf("%.3lf %.3lf",xd, yd);
		}
		std::printf(" %.3lf\n", r);
	}
	return 0;
}

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

int main()
{
	double x1, y1, x2, y2, x3, y3, r, xa, ya, xb, yb, xc, yc;
	double x, y;
	int n;

	cin >> n;
	
	for (int i = 0; i < n; i++){
		cin >> x1 >> y1 >> x2 >> y2 >> x3 >> y3;
		xa = (x2 - x1) * 2;
		xb = (y2 - y1) * 2;
		xc = pow(x1, 2) - pow(x2, 2) + pow(y1, 2) - pow(y2, 2);
		ya = (x3 - x1) * 2;
		yb = (y3 - y1) * 2;
		yc = pow(x1, 2) - pow(x3, 2) + pow(y1, 2) - pow(y3, 2);
		x = (xb * yc - yb * xc) / (xa * yb - ya * xb);
		y = (xc * ya - yc * xa) / (xa * yb - ya * xb);
		r = hypot(x - x1, y - y1);
		printf("%.3lf %.3lf %.3lf", x, y, r);
	}
	return (0);
}

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

using namespace std;

double X1,Y1,X2,Y2,X3,Y3,a,b,c,d,e,f,px,py,r;

int main(){
    int n; scanf( "%d", &n );
    for( int i = 0; i < n; i++ )
    {
        scanf( "%lf %lf %lf %lf %lf %lf", &X1, &Y1, &X2, &Y2, &X3, &Y3 );
        a = ( X2 - X1 ), b = ( Y2 - Y1 ), e = ( a * ( X1 + X2 ) / 2 + b * ( Y1 + Y2 ) / 2 );
        c = ( X3 - X2 ), d = ( Y3 - Y2 ), f = ( c * ( X2 + X3 ) / 2 + d * ( Y2 + Y3 ) / 2 );
        px = ( e * d - b * f ) / ( a * d - b * c ), py = ( a * f - e * c ) / ( a * d - b * c );
        r = ( px - X1 ) * ( px - X1 ) + ( py - Y1 ) * ( py - Y1 );
        r = sqrt( r );
        printf( "%lf %lf %lf\n", px, py, r );
        n--;
    }
    return 0;
}