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 <sstream>
#include <iomanip>
#include <algorithm>
#include <cmath>
#include <string>
#include <vector>
#include <list>
#include <queue>
#include <stack>
#include <set>
#include <map>
#include <bitset>
#include <numeric>
#include <climits>
#include <cfloat>
using namespace std;

double const EPS = 1.0e-10;

class Point
{
public:
    double y, x;
    Point(){
        y = x = 0.0;
    }
    Point(double y0, double x0){
        y = y0;
        x = x0;
    }
    double length() const{
        return sqrt(y * y + x * x);
    }
    double dist(const Point& p) const{
        return sqrt(pow(y - p.y, 2) + pow(x - p.x, 2));
    }
    double dot(const Point& p) const{
        return y * p.y + x * p.x; // |a|*|b|*cosÆ
    }
    double cross(const Point& p) const{
        return x * p.y - y * p.x; // |a|*|b|*sinÆ
    }
    Point operator+(const Point& p) const{
        return Point(y + p.y, x + p.x);
    }
    Point operator-(const Point& p) const{
        return Point(y - p.y, x - p.x);
    }
    Point operator*(double a) const{
        return Point(y * a, x * a);
    }
    Point operator/(double a) const{
        return Point(y / a, x / a);
    }
};

class Line
{
public:
    double a, b, c; // a*x + b*y + c = 0
    Line(double a0, double b0, double c0){
        a = a0;
        b = b0;
        c = c0;
    }
    Line(const Point& p1, const Point& p2){
        double dy = p2.y - p1.y;
        double dx = p2.x - p1.x;
        if(abs(dy / dx) < EPS){
            a = 0.0;
            b = 1.0;
            c = -p1.y;
        }else if(abs(dx / dy) < EPS){
            a = 1.0;
            b = 0.0;
            c = -p1.x;
        }else{
            a = - dy / dx;
            b = 1.0;
            c = dy / dx * p1.x - p1.y;
        }
    }
};

Line perpendicularBisector(const Point& p1, const Point& p2)
{
    return Line(p2.y-p1.y, p2.x-p1.x, (p1.y*p1.y + p1.x*p1.x - p2.y*p2.y - p2.x*p2.x) / 2);
}

bool linesIntersection(const Line& l1, const Line& l2, Point& intersection)
{
    double s = l1.a*l2.b - l2.a*l1.b;
    if(abs(s) < EPS)
        return false;

    intersection = Point(l2.a*l1.c - l1.a*l2.c, l1.b*l2.c - l2.b*l1.c) / s;
    return true;
}

int main()
{
    int n;
    cin >> n;

    while(--n >= 0){
        Point p1, p2, p3;
        cin >> p1.x >> p1.y >> p2.x >> p2.y >> p3.x >> p3.y;

        Line l1 = perpendicularBisector(p1, p2);
        Line l2 = perpendicularBisector(p2, p3);
        Point p;
        linesIntersection(l1, l2, p);

        printf("%.3f %.3f %.3f\n", p.x, p.y, p.dist(p1));
    }

    return 0;
}

C++: #include<complex>
#include<cstdio>
#include<cmath>
using namespace std;
typedef complex<double> P;
#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);
		P 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);
	}
}