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 <math.h>
using namespace std;

int main(void){
    int n;
    double x1, x2, x3, y1, y2, y3, Px, Py, r;
    cin >> n;
    
    for(int i=1; i<=n; i++){
        cin >> x1 >> y1 >> x2 >> y2 >> x3 >> y3;
    
        Px = ( (x1*x1 + y1*y1 - x3*x3 - y3*y3) / (2 * (y1-y3)) - (x2*x2 + y2*y2 - x3*x3 - y3*y3) / (2 * (y2-y3)) ) / ( (x1-x3)/(y1-y3) - (x2-x3)/(y2-y3) );
        Py = -(x1-x3) / (y1-y3) * Px + (x1*x1 + y1*y1 - x3*x3 - y3*y3) / (2 * (y1-y3));
        
        r = sqrt((x1-Px)*(x1-Px) + (y1-Py)*(y1-Py));

        cout << fixed << setprecision(3) << Px << " " << Py << " " << r << endl;
    }
    return 0;
}

C++: #include<iostream>
#include<cmath>
#include<cstdio>
using namespace std;
int main(){
	double a[2],b[2],c[2];
	double matrix[2][2],ans[2],reverse[2][2],det;
	double r,o[2];
	int n;
	cin >>n;
	for(int i=0; i<n; i++){
		cin >>a[0]>>a[1]>>b[0]>>b[1]>>c[0]>>c[1];
		b[0] = b[0]-a[0];
		b[1] = b[1]-a[1];
		c[0] = c[0]-a[0];
		c[1] = c[1]-a[1];
		matrix[0][0] = 2*b[0];
		matrix[1][0] = 2*b[1];
		matrix[0][1] = 2*c[0];
		matrix[1][1] = 2*c[1];
		ans[0] = b[0]*b[0]+b[1]*b[1];
		ans[1] = c[0]*c[0]+c[1]*c[1];
		det = matrix[0][0]*matrix[1][1]-matrix[0][1]*matrix[1][0];
		reverse[0][0] = matrix[1][1]/det;
		reverse[1][0] = -matrix[1][0]/det;
		reverse[0][1] = -matrix[0][1]/det;
		reverse[1][1] = matrix[0][0]/det;
		o[0] = ans[0]*reverse[0][0]+ans[1]*reverse[1][0];
		o[1] = ans[0]*reverse[0][1]+ans[1]*reverse[1][1];
		r = sqrt(o[0]*o[0]+o[1]*o[1]);
		o[0]+=a[0];
		o[1]+=a[1];
		printf("%.3lf %.3lf %.3lf\n",o[0],o[1],r);
	}
	return 0;
}

C++: #include <iostream>
#include <algorithm>
#include <stdio.h>
#include <cmath>

using namespace std;
double min(double x0, double x1, double x2){ return min(min(x0, x1), x2); }
double max(double x0, double x1, double x2){ return max(max(x0, x1), x2); }
double d(double x, double y, double p, double q){ return sqrt((p-x)*(p-x)+(q-y)*(q-y)); }
double diff(double x0, double x1, double x2){ return max(x0,x1,x2)-min(x0,x1,x2); }
int main(){
	int n;
	cin >> n;
	double x[3], y[3];
	for(int j=0; j<n; j++){
	cin >> x[0] >> y[0] >> x[1] >> y[1] >> x[2] >> y[2];
	double ax,ay, r;
	double p, q;
	ax = (max(x[0],x[1],x[2]) + min(x[0],x[1],x[2]))/2;
	ay = (max(y[0],x[1],x[2]) + min(x[0],x[1],x[2]))/2;
	p = (max(x[0],x[1],x[2]) - min(x[0],x[1],x[2]))/4;
	q = (max(y[0],x[1],x[2]) - min(x[0],x[1],x[2]))/4;

	for(int i=0; i<10; i++){
		p = (max(x[0],x[1],x[2]) - min(x[0],x[1],x[2]))/4;
		q = (max(y[0],x[1],x[2]) - min(x[0],x[1],x[2]))/4;
		while(1){
		if(diff(d(x[0],y[0],ax+p,ay),d(x[1],y[1],ax+p,ay),d(x[2],y[2],ax+p,ay)) == diff(d(x[0],y[0],ax-p,ay),d(x[1],y[1],ax-p,ay),d(x[2],y[2],ax-p,ay))){
		}
		else if(diff(d(x[0],y[0],ax+p,ay),d(x[1],y[1],ax+p,ay),d(x[2],y[2],ax+p,ay)) > diff(d(x[0],y[0],ax-p,ay),d(x[1],y[1],ax-p,ay),d(x[2],y[2],ax-p,ay))){
			ax -= p;
		}
		else if(diff(d(x[0],y[0],ax+p,ay),d(x[1],y[1],ax+p,ay),d(x[2],y[2],ax+p,ay)) < diff(d(x[0],y[0],ax-p,ay),d(x[1],y[1],ax-p,ay),d(x[2],y[2],ax-p,ay)) ){
			ax += p;
		}
		if(p<0.000001) break;

		p /= 2;
		}

		while(1){
		if(diff(d(x[0],y[0],ax,ay+q),d(x[1],y[1],ax,ay+q),d(x[2],y[2],ax,ay+q)) == diff(d(x[0],y[0],ax,ay-q),d(x[1],y[1],ax,ay-q),d(x[2],y[2],ax,ay-q))){
		}
		if(diff(d(x[0],y[0],ax,ay+q),d(x[1],y[1],ax,ay+q),d(x[2],y[2],ax,ay+q)) > diff(d(x[0],y[0],ax,ay-q),d(x[1],y[1],ax,ay-q),d(x[2],y[2],ax,ay-q))){
			ax -= q;
		}
		else if(diff(d(x[0],y[0],ax,ay+q),d(x[1],y[1],ax,ay+q),d(x[2],y[2],ax,ay+q)) < diff(d(x[0],y[0],ax,ay-q),d(x[1],y[1],ax,ay-q),d(x[2],y[2],ax,ay-q))){
			ax += q;
		}
		if(q<0.000001) break;

		q /= 2;
		}
	}

	r = d(x[0],y[0],ax,ay);

	printf("%.3f %.3f %.3f\n",ax, ay, r);

}
	return 0;
}