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 <cmath>
#include <cstdio>
#include <vector>
#include <iostream>
#include <algorithm>
using namespace std;
// ------ Classes ------ //
class Point {
public:
	long double px, py;
	Point() : px(0), py(0) {};
	Point(long double px_, long double py_) : px(px_), py(py_) {};
	bool operator==(const Point& p) const { return px == p.px && py == p.py; }
	bool operator!=(const Point& p) const { return px != p.px || py != p.py; }
	bool operator<(const Point& p) const { return px < p.px ? true : (px == p.px && py < p.py); }
	bool operator>(const Point& p) const { return px > p.px ? true : (px == p.px && py > p.py); }
	bool operator<=(const Point& p) const { return !(Point(px, py) > p); }
	bool operator>=(const Point& p) const { return !(Point(px, py) < p); }
	Point operator+(const Point& p) const { return Point(px + p.px, py + p.py); }
	Point operator-(const Point& p) const { return Point(px - p.px, py - p.py); }
	Point operator/(long double d) const { return Point(px / d, py / d); }
	friend Point operator*(const Point p, long double d) { return Point(p.px * d, p.py * d); }
	friend Point operator*(long double d, const Point& p) { return p * d; }
	Point& operator+=(const Point& p1) { px += p1.px, py += p1.py; return *this; }
	Point& operator-=(const Point& p1) { px -= p1.px, py -= p1.py; return *this; }
	Point& operator*=(long double d) { px *= d, py *= d; return *this; }
	Point& operator/=(long double d) { px /= d, py /= d; return *this; }
};
class Circle {
public:
	Point p; long double r;
	Circle() : p(Point()), r(0.0L) {};
	Circle(Point p_) : p(p_), r(0.0L) {};
	Circle(Point p_, long double r_) : p(p_), r(r_) {};
	Circle(long double x_, long double y_) : p(Point(x_, y_)), r(0.0L) {};
	Circle(long double x_, long double y_, long double r_) : p(Point(x_, y_)), r(r_) {};
	bool operator==(const Circle& c) const { return p == c.p && r == c.r; }
	bool operator!=(const Circle& c) const { return !(Circle(p, r) == c); }
};
// ------ Functions ------ //
long double norm(const Point& a) { return a.px * a.px + a.py * a.py; }
long double abs(const Point& a) { return sqrtl(norm(a)); }
long double arg(const Point& a) { return atan2l(a.py, a.px); }
long double dot(const Point& a, const Point& b) { return a.px * b.px + a.py * b.py; }
long double crs(const Point& a, const Point& b) { return a.px * b.py - a.py * b.px; }
long double dst(const Point& a, const Point& b) { return abs(b - a); }
Point pol(long double r, long double d) { return Point(cosl(d) * r, sinl(d) * r); }
vector<Point> crp(Circle c1, Circle c2) {
	double d = abs(c1.p - c2.p);
	double a = acos((c1.r * c1.r + d * d - c2.r * c2.r) / (2 * c1.r * d));
	double t = arg(c2.p - c1.p);
	return{ c1.p + pol(c1.r, t + a), c1.p + pol(c1.r, t - a) };
}
// ------ Main ------ //
int n; Point p1, p2, p3;
int main() {
	cin >> n;
	for (int i = 0; i < n; i++) {
		cin >> p1.px >> p1.py >> p2.px >> p2.py >> p3.px >> p3.py;
		long double d1 = dst(p1, p2), d2 = dst(p2, p3), d3 = dst(p3, p1);
		long double r = d1 * d2 * d3 / sqrtl((d1 + d2 + d3) * (d1 + d2 - d3) * (d2 + d3 - d1) * (d3 + d1 - d2));
		vector<Point> v = crp(Circle(p1, r), Circle(p2, r));
		for (int j = 0; j < v.size(); j++) {
			long double d4 = dst(v[j], p3);
			if (d4 - 1e-10 <= r && r <= d4 + 1e-10) {
				int lx = (v[j].px + 0.00049999L) * 1000;
				int ly = (v[j].py + 0.00049999L) * 1000;
				printf("%.3Lf %.3Lf %.3Lf\n", lx / 1000.0L, ly / 1000.0L, r); break;
			}
		}
	}
	return 0;
}

C++: #include<bits/stdc++.h>
using namespace std;

int main(){

  double x1,y1,x2,y2,x3,y3;
  double px,py;
  int n;

  cin >> n;

  for(int i=0; i<n; i++){
    cin >> x1>>y1>>x2>>y2>>x3>>y3;
    px = ( (y1-y3)*(y1*y1-y2*y2 + x1*x1-x2*x2)-(y1-y2)*(y1*y1-y3*y3+x1*x1-x3*x3))/(2*(y1-y3)*(x1-x2)-2*(y1-y2)*(x1-x3));
    py = ( (x1-x3)*(x1*x1-x2*x2 + y1*y1-y2*y2)-(x1-x2)*(x1*x1-x3*x3+y1*y1-y3*y3))/(2*(x1-x3)*(y1-y2)-2*(x1-x2)*(y1-y3));
    cout << px <<" "<< py <<" ";
    printf("%.3f\n", sqrt((px-x1)*(px-x1)+(py-y1)*(py-y1)));

  }


  return 0;
}