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<cstdlib>
#include<cstring>
#include<cmath>
#include<cassert>
#include<iostream>
#include<sstream>
#include<string>
#include<vector>
#include<queue>
#include<set>
#include<map>
#include<utility>
#include<numeric>
#include<algorithm>
#include<bitset>
#include<complex>

using namespace std;

typedef long long Int;
typedef vector<int> vint;
typedef pair<int,int> pint;
#define mp make_pair

template<class T> void pv(T a, T b) { for (T i = a; i != b; ++i) cout << *i << " "; cout << endl; }
template<class T> void chmin(T &t, T f) { if (t > f) t = f; }
template<class T> void chmax(T &t, T f) { if (t < f) t = f; }
int in() { int x; scanf("%d", &x); return x; }

struct Pt{
	double x,y;
	Pt(){}
	Pt(double x,double y) : x(x),y(y){}
	Pt operator+(const Pt &a) const {return Pt(x+a.x,y+a.y);}
	Pt operator-(const Pt &a) const {return Pt(x-a.x,y-a.y);}
	Pt operator*(const Pt &a) const {return Pt(x*a.x-y*a.y,x*a.y+y*a.x);}
	Pt operator*(const double &k) const {return Pt(x*k,y*k);}
	Pt operator/(const double &k) const {return Pt(x/k,y/k);}
	double abs() const {return sqrt(x*x+y*y);}
	double dot(const Pt &a) const {return x*a.x+y*a.y;}
	double det(const Pt &a) const {return x*a.y-y*a.x;}
};

int main() {
	Pt a,b,c;
	int n;
	n=in();
	int i;
	for(i=0;i<n;i++){
		cin>>a.x>>a.y>>b.x>>b.y>>c.x>>c.y;
		Pt bc=c-b,ca=a-c,ab=b-a;
		Pt res=(b+c-bc*Pt(0,1)*ca.dot(ab)/ca.det(ab))/2;
		printf("%.3f %.3f %.3f\n",res.x,res.y,(res-a).abs());
	}
	return 0;
}

C++: #include<cstdio>
#include<cstdlib>
#include<cstring>
#include<cmath>
#include<ctime>
#include<cctype>
#include<climits>
#include<iostream>
#include<string>
#include<vector>
#include<map>
#include<list>
#include<queue>
#include<deque>
#include<algorithm>
#include<numeric>
#include<utility>
#include<complex>
#include<memory>
#include<functional>

#define REP(i, n) for(int i = 0;i < n;i++)
#define REPR(i, n) for(int i = n;i >= 0;i--)
#define FOR(i, m, n) for(int i = m;i < n;i++)
#define FORR(i, m, n) for(int i = m;i >= n;i--)
#define SORT(v, n) sort(v, v+n);
#define VSORT(v) sort(v.begin(), v.end());
#define llong long long
#define pb(a) push_back(a)
#define INF 999999999
using namespace std;

typedef vector<int> vi;
typedef vector<long long> vl;
typedef vector<double> vd;
typedef pair<int, int> pii;
typedef pair<long, long> pll;
typedef long long ll;

int dy[] = { 0, 0, 1, -1, 0 };
int dx[] = { 1, -1, 0, 0, 0 };


int main(){
	ios::sync_with_stdio(false);

	int n;
	vd x(3), y(3);
	double a1, a2, b1, b2, c1, c2;
	double px, py, r;

	scanf("%d", &n);

	for (; n > 0; n--){
		cin >> x[0] >> y[0] >> x[1] >> y[1] >> x[2] >> y[2];

		a1 = 2 * (x[1] - x[0]);
		b1 = 2 * (y[1] - y[0]);
		c1 = x[0] * x[0] - x[1] * x[1] + y[0] * y[0] - y[1] * y[1];

		a2 = 2 * (x[2] - x[0]);
		b2 = 2 * (y[2] - y[0]);
		c2 = x[0] * x[0] - x[2] * x[2] + y[0] * y[0] - y[2] * y[2];

		px = (b1*c2 - b2*c1) / (a1*b2 - a2*b1);
		py = (c1*a2 - c2*a1) / (a1*b2 - a2*b1);
		r = sqrt((px - x[0])*(px - x[0]) + (py - y[0])*(py - y[0]));

		printf("%.3lf %.3lf %.3lf\n", px, py, r);
	}

}

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

using namespace std;
typedef complex<double> P;

int main(){
  int n;
  scanf("%d",&n);
  while(n--){
    P a,b,c;
    cin >> a.real() >> a.imag() >> b.real() >> b.imag() >> c.real() >> c.imag();
    P m = (a+b)/P(2,0);
    P n = (a+c)/P(2,0);
    P s = (a-b)*P(0,1);
    P t = (a-c)*P(0,1);
    double e = (t.imag()+s.real())/(conj(s)*t).imag();
    P o = m+s*P(e,0);
    double r = abs(a-o);
    printf("%.3f %.3f %.3f",o.real(),o.imag(),r);
  }
}

C++: #include <stdio.h>
#include <math.h>

void solve(double x1, double x2, double x3, double y1, double y2, double y3) {
	double cx1 = (x1+x2)/2.0, cx2 = (x2+x3)/2.0;
	double cy1 = (y1+y2)/2.0, cy2 = (y2+y3)/2.0;
	double tx1 = y1-y2, tx2 = y2-y3;
	double ty1 = x2-x1, ty2 = x3-x2;
	double a=ty1, b=-tx1, c=cx1*ty1-cy1*tx1;
	double d=ty2, e=-tx2, f=cx2*ty2-cy2*tx2;
	double det = a*e-b*d;
	double x = (e*c-b*f)/det;
	double y = (-d*c+a*f)/det;
	double r = sqrt((x1-x)*(x1-x) + (y1-y)*(y1-y));
	printf("%.3f %.3f %.3f\n", x, y, r);
}

int main(void) {
	int n;
	scanf("%d", &n);
	for (int i = 0; i < n; i++) {
		double x1,x2,x3,y1,y2,y3;
		scanf("%lf%lf%lf%lf%lf%lf", &x1, &y1, &x2, &y2, &x3, &y3);
		solve(x1, x2, x3, y1, y2, y3);
	}
	return 0;
}