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>
#define rep(i,n)for(int i=0;i<(n);i++)
using namespace std;

int main() {
	int n; scanf("%d", &n);
	rep(i, n) {
		double x1, y1, x2, y2, x3, y3;
		cin >> x1 >> y1 >> x2 >> y2 >> x3 >> y3;
		double a = -x1 + x2, b = -y1 + y2, c = (-pow(x1, 2) - pow(y1, 2) + pow(x2, 2) + pow(y2, 2)) / 2;
		double d = -x1 + x3, e = -y1 + y3, f = (-pow(x1, 2) - pow(y1, 2) + pow(x3, 2) + pow(y3, 2)) / 2;
		double y = (c*d - a*f) / (b*d - a*e);
		double x = (c - b*y) / a;
		if (isnan(x))abort();
		printf("%.3lf %.3lf %.3lf\n", x, y, hypot(x1 - x, y1 - y));
	}
}

C++: #include<iostream>
#include<math.h>
#include <iomanip>
using namespace std;
int main() {
	int n;
	cin >> n;

	for (int i = 0;i < n;i++) {
		double x1, y1, x2, y2, x3, y3;
		cin >> x1 >> y1 >> x2 >> y2 >> x3 >> y3;

		double px, py, r;
		 double A1, B1, C1, A2, B2, C2;
		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;

		px = (B1*C2 - B2*C1) / (A1*B2 - A2*B1);
		py = (C1*A2 - C2*A1) / (A1*B2 - A2*B1);

		r = sqrt((x1 - px)*(x1 - px) + (y1 - py)*(y1 - py));

		cout << fixed << setprecision(3) << px << " ";
		cout << fixed << setprecision(3) << py << " ";
		cout << fixed << setprecision(3) << r << endl;
	}
	return 0;

}

C++: #include <iostream>
#include <vector>
#include <algorithm>
#include <map>
#include <cmath>
#include <complex>
using namespace std;

typedef double D;
typedef complex<D> P;
const D EPS = 1e-9;
#define X real()
#define Y imag()
#define LE(n,m) ((n) < (m) + EPS)
#define GE(n,m) ((n) + EPS > (m))
#define EQ(n,m) (abs((n)-(m)) < EPS)

D cross(P a, P b) {
  return (conj(a)*b).Y;
}

P crosspointLL(P a1, P a2, P b1, P b2) {
  D d1 = cross(b2-b1, b1-a1);
  D d2 = cross(b2-b1, a2-a1);
  if (EQ(d1, 0) && EQ(d2, 0)) return a1;
  return a1 + d1/d2*(a2-a1);
}

P circumcenter(P a, P b, P c) {
  a = (a-c)*0.5;
  b = (b-c)*0.5;
  return c + crosspointLL(a, a*P(1,1), b, b*P(1,1));
}

int main() {
  int n;
  cin >> n;
  for (int i = 0; i < n; i++) {
    double x1, y1, x2, y2, x3, y3;
    cin >> x1 >> y1 >> x2 >> y2 >> x3 >> y3;

    P a, b, c;
    a = P(x1, y1);
    b = P(x2, y2);
    c = P(x3, y3);
    P ansxy = circumcenter(a, b, c);
    printf("%.3f %.3f %.3f\n", ansxy.X, ansxy.Y, hypot(ansxy.X-x1, ansxy.Y-y1));
  }

}

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

int main() {
    int n;
    cin >> n;
    while(n--) {
        double x1, x2, x3, y1, y2, y3;
        cin >> x1 >> y1 >> x2 >> y2 >> x3 >> y3;
        double a1, a2, b1, b2, c1, c2,x, y, r;
        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;
        
        x = (double)(b1*c2-b2*c1)/(double)(a1*b2-a2*b1);
        y = (double)(c1*a2-c2*a1)/(double)(a1*b2-a2*b1);
        r = (double)sqrt((x-x1)*(x-x1)+(y-y1)*(y-y1));
        
        cout << x << " " << y << " " << r << endl;
    }
    return 0;
}

C++: #include<complex>
#include<cstdio>
#include<cmath>
using namespace std;typedef complex<double> P;class Tr{P a,b,c;double A,B,C;double x,y,z;double F(double a,double b, double c){return acos((b*b+c*c-a*a)/(2*b*c));}public:Tr(P p1, P p2, P p3){a=p1;b=p2;c=p3;B=abs(c-a);A=abs(b-c);C=abs(a-b);x=F(A,B,C);y=F(B,C,A);z=F(C,A,B);}double R(){return A/sin(x)/2.;}double X(){double A=sin(2*x),B=sin(2*y),C=sin(2*z);return(a.real()*A+b.real()*B+c.real()*C)/(A+B+C);}double Y(){double A=sin(2*x),B=sin(2*y),C=sin(2*z);return(a.imag()*A+b.imag()*B+c.imag()*C)/(A+B+C);}};int main(){int n;double d,e,f,g,h,i;scanf("%d",&n);for(;n--;){scanf("%lf%lf%lf%lf%lf%lf",&d,&g,&e,&h,&f,&i);P a(d,g),b(e,h),c(f,i);Tr T(a,b,c);printf("%.3f %.3f %.3f\n",T.X(),T.Y(),T.R());}}