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<stdio.h>
#include<math.h>
#define P(x) pow(double(x),2)
 
 
 
int main(){
 
 
    int i,j,k;
    int n;
    double x[3],y[3];
    double xp,yp,r;
    double a1,a2,b1,b2,c1,c2;
     
    while((scanf("%d",&n))!=EOF){
        for(i=0;i<3;i++){
            scanf("%lf",&x[i]);
            scanf("%lf",&y[i]);
        }
        a1=2*(x[1]-x[0]);
        a2=2*(x[2]-x[1]);
        b1=2*(y[1]-y[0]);
        b2=2*(y[2]-y[1]);
        c1=(P(x[0])-P(x[1])+P(y[0])-P(y[1]));
        c2=(P(x[1])-P(x[2])+P(y[1])-P(y[2]));
     
        xp=(b1*c2-b2*c1)/(a1*b2-a2*b1);
        yp=(c1*a2-c2*a1)/(a1*b2-a2*b1);
        r=(double)(sqrt((long double)(((xp-x[0])*(xp-x[0]))+((yp-y[0])*(yp-y[0])))));  
 
 
        printf("%.3f %.3f %.3f\n",xp,yp,r);
 
    }
 
 
 
}

C++: #include <iostream>
#include <cmath>
#include <cstdio>

int main()
{
    std::ios::sync_with_stdio(false);
    std::cin.tie(0);

    int n;
    std::cin >> n;
    while (n--) {
        /* A(x1, y1)
         * B(x2, y2)
         * C(x3, y3)
         * */
        double x1, y1, x2, y2, x3, y3;
        double px, py, r;
        double radA, radB, radC;
        double a, b, c;
        std::cin >> x1 >> y1 >> x2 >> y2 >> x3 >> y3;
        a = std::sqrt(std::pow(x3 -  x2, 2) + std::pow(y3 - y2, 2));
        b = std::sqrt(std::pow(x1 -  x3, 2) + std::pow(y1 - y3, 2));
        c = std::sqrt(std::pow(x2 -  x1, 2) + std::pow(y2 - y1, 2));
        radA = std::acos((b*b + c*c - a*a) / (2*b*c));
        radB = std::acos((c*c + a*a - b*b) / (2*c*a));
        radC = std::acos((a*a + b*b - c*c) / (2*a*b));
        double sin2A = std::sin(2*radA);
        double sin2B = std::sin(2*radB);
        double sin2C = std::sin(2*radC);
        px = (sin2A*x1 + sin2B*x2 + sin2C*x3) / (sin2A + sin2B + sin2C);
        py = (sin2A*y1 + sin2B*y2 + sin2C*y3) / (sin2A + sin2B + sin2C);
        r = a / (2 * std::sin(radA));
        std::printf("%.3lf %.3lf %.3lf\n", px, py, r);
        //std::printf("(x1,y1)=(%.1lf,%.1lf)\n(x2,y2)=(%.1lf,%.1lf)\n(x3,y3)=(%.1lf,%.1lf)\n", x1, y1, x2, y2, x3, y3);
        //std::printf("a:%.3lf b:%.3lf c:%.3lf\n", a, b, c);
        //std::printf("radA:%.3lf radB:%.3lf radC:%.3lf\n", radA, radB, radC);
        //std::printf("A:%.3lf B:%.3lf C:%.3lf\n", radA * 180 / M_PI, radB * 180 / M_PI, radC * 180 / M_PI);
    }
}

C++: #include <iostream>
#include <cstdio>
#include <cmath>
#include <vector>
#include <map>
#include <stack>
#include <queue>
#include <algorithm>
#include <set>

#define FOR(i,a,b) for(int i=(a);i<(b);i++)
#define REP(i,j) FOR(i,0,j)
#define mp std::make_pair

const int INF = 1 << 24;
const int dx[4] = {0, 0, 1, -1}, dy[4] = {1, -1, 0, 0};

typedef unsigned long long ull;

struct P{
    double x, y;
    double size(){
        return std::sqrt(x*x + y*y);
    }
    double sizeS(){
        return x*x + y*y;
    }
};

P operator+(const P& lp, const P& rp){
    return {lp.x+rp.x, lp.y+rp.y};
}

P operator-(const P& lp, const P& rp){
    return {lp.x-rp.x, lp.y-rp.y};
}

P operator*(const P& p, const double& k){
    return {k*p.x, k*p.y};
}

double cross(const P& lp, const P& rp){
    return lp.x * rp.y - lp.y * rp.x;
}

int main(){
    int N;
    std::cin >> N;

    REP(i, N){
        P A, B, C, v1, v2, v3;
        std::cin >> A.x >> A.y >> B.x >> B.y >> C.x >> C.y;
        v1 = B - A; v2 = C - A, v3 = B - C;

        double sinA = std::abs(cross(v1, v2)) / (v1.size() * v2.size()),
            r = v3.size() / 2.0 / sinA;

        double x = 0.5 * ((A.y-C.y)*(A.sizeS()-B.sizeS()) - (A.y-B.y)*(A.sizeS()-C.sizeS())) / ((A.x-B.x)*(A.y-C.y)-(A.x-C.x)*(A.y-B.y)),
            y = 0.5 * ((A.x-C.x)*(A.sizeS()-B.sizeS()) - (A.x-B.x)*(A.sizeS()-C.sizeS())) / ((A.y-B.y)*(A.x-C.x)-(A.y-C.y)*(A.x-B.x));

        printf("%.3f %.3f %.3f\n", x, y, r);
    }
}