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<bits/stdc++.h>
using namespace std;

struct Point{double x, y;};

Point center2(Point p1, Point p2, Point p3){
	Point p;
	if(p1.y == p2.y){
		p.x = (p1.x + p2.x) / 2.0;
	}else if(p2.y == p3.y){
		p.x = (p2.x + p3.x) / 2.0;
	}
	p.y = p.x - (p2.x + p3.x) / 2.0;
	p.y *= -(p3.x - p2.x) / (p3.y - p2.y);
	p.y += (p2.y + p3.y) / 2.0;
	return p;
}

Point center(Point p1, Point p2, Point p3){
	if(p1.y == p2.y || p2.y == p3.y) return center2(p1, p2, p3);
	Point p;
	p.x = 0.0;
	p.x += (p3.y - p1.y) / 2.0;
	p.x -= (p2.x * p2.x - p1.x * p1.x) / (2.0 * (p2.y - p1.y));
	p.x += (p3.x * p3.x - p2.x * p2.x) / (2.0 * (p3.y - p2.y));
	p.x /= ((p3.x - p2.x) / (p3.y - p2.y) - (p2.x - p1.x) / (p2.y - p1.y));
	p.y = p.x - (p2.x + p3.x) / 2.0;
	p.y *= -(p3.x - p2.x) / (p3.y - p2.y);
	p.y += (p2.y + p3.y) / 2.0;
	return p;
}

int main(){
	int n;
	Point p1, p2, p3;
	Point p;
	double r;
	scanf("%d", &n);
	for(int i = 0; i < n; i++){
		scanf("%lf %lf %lf %lf %lf %lf", &p1.x, &p1.y, &p2.x, &p2.y, &p3.x, &p3.y);
		p = center(p1, p2, p3);
		r = sqrt((p.x - p1.x) * (p.x - p1.x) + (p.y - p1.y) * (p.y - p1.y));
		printf("%.4lf %.4lf %.4lf\n", p.x, p.y, r);
	}
	return 0;
}

C++: #include<iostream>
#include<iomanip>
#include<cmath>
#define PI 3.14159265359
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 )));


		if( a >= PI ) a=2*PI-a;
		if( b >= PI ) b=2*PI-b;
		if( c >= PI ) c=2*PI-c;


		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*1000+0.5)/1000;
		px = floor(px*1000+0.5)/1000;
		py = floor(py*1000+0.5)/1000;

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

	}
	return 0;
}

C++: #include<complex>
#include<stdio.h>
#include<cmath>
#define F(a,b,c) acos((b*b+c*c-a*a)/2/b/c)
int main(){
	int n;double d,e,f,g,h,i;
	for(scanf("%d",&n);n--;){
		scanf("%lf%lf%lf%lf%lf%lf",&d,&g,&e,&h,&f,&i);
		std::complex<double> a(d,g),b(e,h),c(f,i);
		double A=abs(b-c),B=abs(c-a),C=abs(a-b),
		s=sin(2*F(A,B,C)),t=sin(2*F(B,C,A)),u=sin(2*F(C,A,B)),v=s+t+u;
		printf("%.3f %.3f %.3f\n",(d*s+e*t+f*u)/v,(g*s+h*t+i*u)/v,A/sin(F(A,B,C))/2);
	}
}

C++: #include <stdio.h>
#include <math.h>

int main(){
	int n;
	scanf("%d", &n);
	for(int i = 0; i < n; i++){
		float x1, y1, x2, y2, x3, y3;
		scanf("%f %f %f %f %f %f", &x1, &y1, &x2, &y2, &x3, &y3);
		float a = (x2 - x3)*(x2 - x3) + (y2 - y3)*(y2 - y3);
		float b = (x1 - x3)*(x1 - x3) + (y1 - y3)*(y1 - y3);
		float c = (x1 - x2)*(x1 - x2) + (y1 - y2)*(y1 - y2);
		float s = ((x2-x1)*(y3-y1) - (x3-x1)*(y2-y1)) / 2;
		float x = (a*(b + c - a)*x1 + b*(c + a - b)*x2 + c*(a + b - c)*x3) / (16*s*s);
		float y = (a*(b + c - a)*y1 + b*(c + a - b)*y2 + c*(a + b - c)*y3) / (16*s*s);
		float r = sqrt((x-x1)*(x-x1) + (y-y1)*(y-y1));
		printf("%.3f %.3f %.3f\n", x, y, r);
	}
	return 0;
}