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<cstdio>
#include<algorithm>
#include<vector>
#include<string>
#include<iostream>
#include<queue>
#include<map>
#include<set>
#include<complex>

using namespace std;

#define reps(i,f,n) for(int i=f;i<int(n);i++)
#define rep(i,n) reps(i,0,n)

#define X real()
#define Y imag()

typedef complex<double> P;
class C:public P{
	public:
	double r;
	C(double x,double y,double r):P(x,y),r(r){}
};

template<class T> sq(T x){return x*x;}
double dot(P a, P b){return a.X*b.X + a.Y*b.Y;}

P solve_eq2(double a,double b,double c,double d,double e,double f){
	double A = a*e-b*d;
	return P((c*e-b*f)/A, (a*f-c*d)/A);
}

C C_PPP(P a,P b,P c){
	P d = b-a;
	P e = c-a;
	
	double z1 = -dot(a,a);
	double z2 = -dot(b,b);
	double z3 = -dot(c,c);
	
	P f = solve_eq2(d.X, d.Y, z2-z1, e.X, e.Y, z3-z1);
	double u = z1-dot(a,f);
	
	return C(-f.X/2, -f.Y/2, sqrt(dot(f,f)/4-u));
}

int main(){
	
	int n;
	cin>>n;
	
	rep(i,n){
		double xa,ya,xb,yb,xc,yc;
		cin>>xa>>ya>>xb>>yb>>xc>>yc;
		
		C circle = C_PPP(P(xa,ya),P(xb,yb),P(xc,yc));
		
		printf("%.3lf %.3lf %.3lf\n",circle.X,circle.Y,circle.r);
	}
}

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

using namespace std;

int main(){
	
    int n;
    cin >> n;
    while(n--) {
    	
        double x1, y1, x2, y2, x3, y3;
        cin >> x1 >> y1 >> x2 >> y2 >> x3 >> y3;
        
        double a1 = 2 * (x2 - x1);
        double b1 = 2 * (y2 - y1);
        double c1 = x1 * x1 -x2 * x2 + y1 * y1 - y2 * y2;
        
        double a2 = 2 * (x3 - x1);
        double b2 = 2 * (y3 - y1);
        double c2 = x1 * x1 - x3 * x3 + y1 * y1 - y3 * y3;
        
        double x = (b1  *c2 - b2 * c1) / (a1 * b2 - a2 * b1);
        double y = (c1 * a2 - c2 * a1) / (a1 * b2 - a2 * b1);
        double r = hypot(x-x1, y-y1);
        
        cout << fixed << setprecision(3) 
        	 << x << " " << y << " " << r << "\n";
        
    }
    return 0;
}

C++: #include<bits/stdc++.h>
using namespace std;

const double EPS = 1e-8;
const double INF = 1e12;
const double PI = acos(-1);

using Point = complex<double>;
using Polygon = vector<Point>;

inline int sgn(const double &a) { return (a < -EPS ? -1 : (a > EPS ? 1 : 0)); }

inline bool eq(const Point &a, const Point &b) { return abs(a - b) < EPS; }

inline bool operator<(const Point &a, const Point &b){
    if (sgn(a.real() - b.real()))
        sgn(a.real() - b.real()) < 0;
    return sgn(a.imag() - b.imag());
}

double dot(const Point &a, const Point &b) { return real(conj(a) * b); }

double det(const Point &a, const Point &b) { return imag(conj(a) * b); }

struct Line {
    Point p1, p2;

    Line(Point p1 = Point(), Point p2 = Point()) : p1(p1), p2(p2) {}

    bool operator<(const Line &rhs) const {
        if (eq(p2, rhs.p2))
            return p1 < rhs.p1;
        return p2 < rhs.p2;
    }
    bool operator==(const Line &rhs) const {
        return (eq(p1, rhs.p1) && eq(p2, rhs.p2)) ||
               (eq(p1, rhs.p2) && eq(p2, rhs.p1));
    }
};

Point circumcenter(Point p1, Point p2, Point p3) {
  double a1, b1, c1, a2, b2, c2, cx, cy;
  a1 = real(p2 - p1);
  b1 = imag(p2 - p1);
  c1 = norm(p2) - norm(p1);
  a2 = real(p3 - p2);
  b2 = imag(p3 - p2);
  c2 = norm(p3) - norm(p2);
  cx = (b2 * c1 - b1 * c2) / (2.0 * (a1 * b2 - a2 * b1));
  cy = (a1 * c2 - a2 * c1) / (2.0 * (a1 * b2 - a2 * b1));
  return Point(cx, cy);
}

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;
        Point c = circumcenter(Point(x1,y1),Point(x2,y2),Point(x3,y3));
        double r = abs(Point(x1,y1) - c);
        printf("%.3f %.3f %.3f\n",c.real(),c.imag(),r);
    }

    return 0;
}

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

int main(){
	int a;
	scanf("%d",&a);
	while(a--){
		double x1,y1,x2,y2,x3,y3;
		scanf("%lf%lf%lf%lf%lf%lf",&x1,&y1,&x2,&y2,&x3,&y3);
		double a1 = 2*(x2 - x1), b1 = 2*(y2 - y1);
		double c1 = x1*x1 - x2*x2 + y1*y1 - y2*y2;
		double a2 = 2*(x3-x1), b2 = 2*(y3-y1);
		double c2 = x1*x1 - x3*x3 + y1*y1 - y3*y3;
		double x = (b1*c2 - b2*c1)/(a1*b2 - a2*b1);
		double y = (c1*a2 - c2*a1)/(a1*b2 - a2*b1);
		double r = hypot(x-x1,y-y1);
		printf("%.3lf %.3lf %.3lf\n",x,y,r);
	}
}