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<cstdio>
#include<algorithm>
#include<cmath>
#include<vector>
#include<iomanip>
using namespace std;
static const int COUNTER_CLOCKWISE = 1;
static const int CLOCKWISE = -1;
static const int ONLINE_BACK = 2;
static const int ONLINE_FRONT = -2;
static const int ON_SEGMENT = 0;
 
#define EPS (1e-10)
#define equals(a, b) (fabs((a) - (b)) < EPS)
 
class Point{
    public:
        double x, y;
 
        Point(double x = 0, double y = 0): x(x), y(y) {}
 
        Point operator + (Point p){ return Point(x + p.x, y + p.y);}
        Point operator - (Point p){ return Point(x - p.x, y - p.y);}
        Point operator * (double a){ return Point(a * x, a * y);}
        Point operator / (double a){ return Point(x / a, y / a);}
 
        double abs(){ return sqrt(norm());}
        double norm(){ return x * x + y * y;}
 
        bool operator < (const Point &p) const{
            return x != p.x ? x < p.x : y < p.y;
        }
 
        bool operator == (const Point &p) const{
            return fabs(x - p.x) < EPS && fabs(y - p.y) < EPS;
        }
};
 
struct Segment {
    Point p1, p2;
};
typedef Segment Line;
 
class Circle{
    public:
        Point c;
        double r;
        Circle(Point c = Point(), double r = 0.0): c(c), r(r) {}
};
 
typedef Point Vector;
typedef vector<Point> Polygon;
 
double dot(Vector a, Vector b){
    return a.x * b.x + a.y * b.y;
}
double cross(Vector a, Vector b){
    return a.x * b.y - a.y * b.x;
}
 
Point project(Segment s, Point p){
    Vector base = s.p2 - s.p1;
    double r = dot(p - s.p1, base) / base.norm();
    return s.p1 + base * r;
}
 
Point getCrossPoint(Segment s1, Segment s2){
    Vector base = s2.p2 - s2.p1;
    double d1 = abs(cross(base, s1.p1 - s2.p1));
    double d2 = abs(cross(base, s1.p2 - s2.p1));
    double t = d1 / (d1 + d2);
    return s1.p1 + (s1.p2 - s1.p1) * t;
}
 
double getDistance(Point a, Point b){
    return (a - b).abs();
}
 
pair<Point, Point> getCrossPoints(Circle c, Line l){
    Vector pr = project(l, c.c);
    Vector e = (l.p2 - l.p1) / (l.p2 - l.p1).abs();
    double base = sqrt(c.r * c.r - (pr - c.c).norm());
    return make_pair(pr + e * base, pr - e * base);
}
 
double arg(Vector p){return atan2(p.y, p.x);}
Vector polar(double a, double r){return Point(cos(r) * a, sin(r) * a);}
 
pair<Point, Point> getCrossPoints(Circle c1, Circle c2){
    double d = (c1.c - c2.c).abs();
    double a = acos((c1.r * c1.r + d * d - c2.r * c2.r) / (2 * c1.r * d));
    double t = arg(c2.c - c1.c);
    return make_pair(c1.c + polar(c1.r, t + a), c1.c + polar(c1.r, t - a));
}
 
int main(){
    int n;
    Point p[3];
    cin >> n;
    for(int i = 1; i <= n; i++){
        for(int j = 0; j < 3; j++){
            cin >> p[j].x >> p[j].y;
        }
        pair<Point, Point> pp = getCrossPoints((Circle){p[0], 400.0}, (Circle){p[1], 400.0});
        pair<Point, Point> pp2 = getCrossPoints((Circle){p[0], 400.0}, (Circle){p[2], 400.0});
        Point P = getCrossPoint((Line){pp.first, pp.second}, (Line){pp2.first, pp2.second});
        cout << P.x << " " << P.y << " " << getDistance(p[0], P) << endl;
    }
    return 0;
}

C++: #include <iostream>
#include <cmath>
#include <cstdio>
using namespace std;
typedef pair<double, double> PDD;
PDD calc(double mat[2][2], double vec[2]){
  double a = mat[0][0], b = mat[0][1], d = mat[1][0], e = mat[1][1];
  double c = vec[0], f = vec[1];
  double det = a * e - d * b;
  return make_pair((e * c - b * f) / det, (-c * d + a * f) / det);
}
int main(){
  int Tc;
  cin >> Tc;
  for(int tc = 0; tc < Tc; ++tc){
    double x1, y1, x2, y2, x3, y3;
    cin >> x1 >> y1 >> x2 >> y2 >> x3 >> y3;
    double A, B, C, D, E, F;
    A = (y1 + y3) / 2.;
    B = (x1 - x3) / (y1 - y3);
    C = (x1 + x3) / 2.;
    D = (y2 + y3) / 2.;
    E = (x2 - x3) / (y2 - y3);
    F = (x2 + x3) / 2.;
    double mat[2][2];
    mat[0][0] = B; mat[0][1] = 1;
    mat[1][0] = E; mat[1][1] = 1;
    double vec[2];
    vec[0] = A + B * C;
    vec[1] = D + E * F;
    PDD res = calc(mat, vec);
    double x = res.first, y = res.second;
    double r = pow((x-x1)*(x-x1)+(y-y1)*(y-y1), 0.5);
    x = (double)(round(x*1000))/1000.0;
    y = (double)(round(y*1000))/1000.0;
    r = (double)(round(r*1000))/1000.0;
    printf("%.3f %.3f %.3f\n", x, y, r);
  }
  return 0;
}