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;

const double EPS = 1e-8;
const double INF = 1e12;
typedef complex<double> P;
namespace std {
    bool operator < (const P& a, const P& b) {
        return real(a) != real(b) ? real(a) < real(b) : imag(a) < imag(b);
    }
}
double cross(const P& a, const P& b) {
    return imag(conj(a)*b);
}
double dot(const P& a, const P& b) {
    return real(conj(a)*b);
}

typedef vector<P> G;

double area2(const G& P) {
    double A = 0;
    for (int i = 0; i < P.size(); ++i)
        A += cross(P[i], P[(i+1)%P.size()]);
    return A;
}

int main(){
    double x, y;
    G g;
    while(scanf("%lf,%lf", &x, &y) != EOF){P p(y, x); g.push_back(p);}
    printf("%lf\n", abs(area2(g)/2.));
}

C++: #include <iostream>
#include <cstdio>
#include <cmath>
using namespace std;

float a, b, c, d, e, f;
float x, y;
float rx, ry;


float RoundNumber(float f) {
  int tf = (int)(10000 * f);
  if (tf % 10 >= 5) {
    tf += 10;
  }
  tf /= 10;
  return (float)tf / 1000.0f;
}

void solve(){
  float tmp1 = f-(c*d/a);
  float tmp2 = e-(b*d/a);
  y = tmp1/tmp2;
  x = (c - b * y) / a;  
  printf("%.3f %.3f ", RoundNumber(x), RoundNumber(y));        
}

int main(int argc, char const* argv[]) {
  int n;
  cin>>n;
  for (int i = 0; i < n; i += 1) {
    float x1, y1, x2, y2, x3, y3;
    cin>>x1>>y1>>x2>>y2>>x3>>y3;
    a = -2*x1 + 2*x2;
    b = -2*y1 + 2*y2;
    c = x2*x2 + y2*y2 - x1*x1 - y1*y1;
    d = -2*x1 + 2*x3;
    e = -2*y1 + 2*y3;
    f = x3*x3 + y3*y3 - x1*x1 - y1*y1;

    solve();
    
    float r = (x - x1)*(x - x1) + (y - y1)*(y - y1);
    r = sqrt(r);
    printf("%.3f\n", RoundNumber(r));
  }  
  return 0;
}

C++: #include<stdio.h>
#include<iostream>
#include<math.h>
#include<iomanip>
using namespace std;

int main()
{
	int n; cin >> n;
	double x[3];
	double y[3];
	double r;

	while(n--){
	 for(int j=0;j<3;j++){
	 	cin >> x[j] >> y[j];
	 }

	 double a = 2*(x[1]-x[0]);
	 double b = 2*(y[1]-y[0]);
	 double c = 2*(x[2]-x[0]);
	 double d = 2*(y[2]-y[0]);

	 double e = pow(x[1],2.0)-pow(x[0],2.0)+pow(y[1],2.0)-pow(y[0],2.0);
	 double f = pow(x[2],2.0)-pow(x[0],2.0)+pow(y[2],2.0)-pow(y[0],2.0);

	 if(a==0){
	 	swap(a,c);
	 	swap(b,d);
	 	swap(e,f);
	 }

	b = b/a;
	e = e/a;
	a = a/a;
	 
	 
	d = d-b*c;
	f = f-e*c;
	c = c-a*c;

	f = f/d;
	d = d/d;

	b = b-d*b;
	e = e-f*b;

	r = sqrt(pow((e-x[0]),2.0)+pow((f-y[0]),2.0));
	
	cout << fixed;
	cout << setprecision(3) << e <<" "<< f << " " << r << endl;
	}
	return 0;

}