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 <algorithm>

using namespace std;

int main()
{
	double A1, B1, C1, A2, B2, C2;
	double X1, X2, X3, Y1, Y2, Y3;
	double X, Y, R;

	int n;
	cin>>n;

	for(int i = 0; i < n; i++){
		cin>>X1>>Y1>>X2>>Y2>>X3>>Y3;

		A1=2*(X2-X1);
		B1=2*(Y2-Y1);
		C1=pow(X1,2)-pow(X2,2)+pow(Y1,2)-pow(Y2,2);
		A2=2*(X3-X1);
		B2=2*(Y3-Y1);
		C2=pow(X1,2)-pow(X3,2)+pow(Y1,2)-pow(Y3,2);

		X = (B1*C2-B2*C1)/(A1*B2-A2*B1);
		Y = (C1*A2-C2*A1)/(A1*B2-A2*B1);

		R = sqrt(pow(max(X,X1)-min(X,X1),2)+pow(max(Y,Y1)-min(Y,Y1),2));

		if(X >= 0) X = ((double)((int)(X*1000+0.5)))/1000;
		else X = ((double)((int)(X*1000-0.5)))/1000;
		if(Y >= 0) Y = ((double)((int)(Y*1000+0.5)))/1000;
		else Y = ((double)((int)(Y*1000-0.5)))/1000;
		if(R >= 0) R = ((double)((int)(R*1000+0.5)))/1000;
		else R = ((double)((int)(R*1000-0.5)))/1000;

		printf("%.3f %.3f %.3f",X, Y, R);
	}
}

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

int main(){

	int n;
	double x1, y1, x2, y2, x3, y3;
	double la, lb, lc;
	double a, b, c;
	
	double r;
	double px, py;

	cin >> n;

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

		//lc = (x1 - x2) * (x1 - x2) + (y1 - y2) * (y1 - y2);
		la = (x2 - x3) * (x2 - x3) + (y2 - y3) * (y2 - y3);
		//lb = (x3 - x1) * (x3 - x1) + (y3 - y1) * (y3 - y1);

		a = fabs((atan2( y2 - y1, x2 - x1 ) - atan2( y3 - y1, x3 - x1 )));
		b = fabs((atan2( y1 - y2, x1 - x2 ) - atan2( y3 - y2, x3 - x2 )));
		c = fabs((atan2( y1 - y3, x1 - x3 ) - atan2( y2 - y3, x2 - x3 )));

		r = sqrt(la) / (sin(a)*2);
		px = ( sin(2*a) * x1 + sin(2*b) * x2 + sin(2*c) * x3 ) / (sin(2*a)+sin(2*b)+sin(2*c));
		py = ( sin(2*a) * y1 + sin(2*b) * y2 + sin(2*c) * y3 ) / (sin(2*a)+sin(2*b)+sin(2*c));

		r = floor(r*10000+0.5)/10000;
		px = floor(px*10000+0.5)/10000;
		py = floor(py*10000+0.5)/10000;

		cout << setprecision(3) << fixed  << px << " " << py << " " << r << endl;

	}
	return 0;
}