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>

using namespace std;

class Vector{
public:
	double x;
	double y;

	Vector(){}
	Vector( double dx, double dy ){
		x = dx;
		y = dy;
	}

	double operator*( const Vector& hoge ){
		return x * hoge.x + y * hoge.y;
	}

	Vector operator*( const double hoge )
	{
		return Vector( x * hoge, y * hoge );
	}

	Vector operator/( const double hoge )
	{
		return Vector( x / hoge, y / hoge );
	}

	Vector operator-( const Vector& hoge ){
		return Vector( x - hoge.x, y - hoge.y );
	}

	Vector operator-(){
		return Vector( -x, -y );
	}

	Vector operator+( const Vector& hoge ){
		return Vector( x + hoge.x, y + hoge.y );
	}
};

double change( double data )
{
	data *= 1000;
	data = int( data + .5 -( data < 0 ) );
	data /= 1000;
	return data;
}

int main(int argc, char const* argv[])
{
	Vector p1,p2,p3,circ;
	double r;
	int n;

	cin >> n;
	for( int i = 0;i < n;i++ ){
		cin >> p1.x >> p1.y >> p2.x >> p2.y >> p3.x >> p3.y;
		Vector e1,e2,e3;
		e1 = p3 - p2;
		e2 = p1 - p3;
		e3 = p2 - p1;

		double d1 = (-e2) * e3;
		double d2 = (-e3) * e1;
		double d3 = (-e1) * e2;
		double c1 = d2 * d3;
		double c2 = d3 * d1;
		double c3 = d1 * d2;
		double c = c1 + c2 + c3;

		circ = ( (p1 * (c2 + c3)) + (p2 * (c3 + c1)) + (p3 * (c1 + c2)) ) / (2 * c);
		r = sqrt( fabs((d1 + d2) * (d2 + d3) * (d3 + d1) / c) ) / 2;
		circ.x = change( circ.x );
		circ.y = change( circ.y );
		r = change( r );

		printf("%.3f %.3f %.3f\n",circ.x, circ.y, r );
	}

	return 0;
}

C++: #include<iostream>
#include<cstdio>
#include<cmath>
#include<string>
#include<algorithm>
using namespace std;
#define int long long

signed main(){

        int n;
        scanf("%lld",&n);
        for(int i=0;i<n;i++){
                double x1,x2,x3,y1,y2,y3;
                scanf("%lf %lf %lf %lf %lf %lf", &x1, &y1, &x2, &y2, &x3, &y3);
                double t1 = atan2(x2-x1,y2-y1);
                double t2 = atan2(x3-x1,y3-y1);
                double d = sqrt((x3-x2)*(x3-x2)+(y3-y2)*(y3-y2));
                double r = d/sin(abs(t1-t2))/2;
                double d2 = sqrt(r*r-d*d/4);
                double xc = (x3+x2)/2 - (y3-y2)/d*d2;
                double yc = (y3+y2)/2 - (x3-x2)/d*d2;
                printf("%.3f %.3f %.3f\n", xc,yc, r);

        }

        return 0;
}

C++: #include<iostream>
#include<math.h>
#include<iomanip>
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;
		double a,b,c,d,e,f;
		a=-2*(x1-x2);
		b=-2*(y1-y2);
		c=x1*x1+y1*y1-x2*x2-y2*y2;
		d=-2*(x1-x3);
		e=-2*(y1-y3);
		f=x1*x1+y1*y1-x3*x3-y3*y3;
		double x,y,r;
		x=(b*f-c*e)/(a*e-b*d);
		y=(c*d-a*f)/(a*e-b*d);
		r=(x-x1)*(x-x1)+(y-y1)*(y-y1);
		r=sqrt(r);
		cout<<fixed<<setprecision(3)
			<<x<<" "<<y<<" "<<r<<endl;
	}
}