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;
#define mp make_pair
#define fi first
#define se second
#define ll long long
#define pb push_back

# define inOut(a,b) freopen(a,"r",stdin);freopen(b,"w",stdout);
# define RESET(a) memset(a,0,sizeof(a))
# define MEMO(a) memset(a,-1,sizeof(a))
# define DEBUG puts("Debug-Has-Come-Until-Here")


typedef pair<int,int> ii;
typedef vector<int> vi;
typedef vector<ii> vii;

int main(){
	cin.tie(NULL);

	double x1, x2, x3, y1, y2, y3;
	double a,b,c,d,e,f;
	double x,y;
	int dummy;
	
	scanf("%d", &dummy);
	while(scanf("%lf %lf %lf %lf %lf %lf", &x1, &y1, &x2, &y2, &x3, &y3) != EOF){
		a = -2*x1 + 2*x2;
		b = -2*y1 + 2*y2;
		c = (x2*x2 - x1*x1) + (y2*y2 - y1*y1);
		d = -2*x2 + 2*x3;
		e = -2*y2 + 2*y3;
		f = (x3*x3 - x2*x2) + (y3*y3-y2*y2);
		
		x = (c*e - b*f)/(a*e-b*d);
		y = (c*d - a*f)/(b*d-e*a);
		printf("%.3lf %.3lf %.3lf\n", x, y, sqrt((x-x1)*(x-x1)+(y-y1)*(y-y1)));
	}

	return 0;
}

C++: using namespace std;
 
int main(){
   
 int cnt;
    cin >> cnt;
   ??? double x1, y1, x2, y2, x3, y3;
    ???double a1, a2, b1, b2, c1, c2;
    ???double xp, yp, r;

    while (cnt > 0 && cin >> x1 >> y1 >> x2 >> y2 >> x3 >> y3) {
        a1 = 2 * (x2 - x1);
        b1 = 2 * (y2 - y1);
        c1 = x1 * x1 - x2 * x2 + y1 * y1 - y2 * y2;
        a2 = 2 * (x3 - x1);
        b2 = 2 * (y3 - y1);
        c2 = x1 * x1 - x3 * x3 + y1 * y1 - y3 * y3;
        xp = (double)((b1*c2 - b2*c1) / (a1*b2 - a2*b1) * 1000) / 1000.0;
        yp = (double)((c1*a2 - c2*a1) / (a1*b2 - a2*b1) * 1000) / 1000.0;
//

        r = hypot(xp - x1, yp - y1);
 
        cout<< setprecision(3)<< xp << " " << yp << " " << r << endl;
        cnt -= 1;
    }
    return 0;
}