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 <iostream>
#include <iomanip>
#include <sstream>
#include <cstdio>
#include <cstdlib>
#include <cmath>
#include <cstring>
#include <climits>
#include <cfloat>
#include <string>
#include <vector>
#include <stack>
#include <queue>
#include <set>
#include <map>
#include <bitset>
#include <algorithm>
#include <functional>
#include <utility>
#include <numeric>

using namespace std;

typedef unsigned int UI;
typedef long long LL;
typedef unsigned long long ULL;
typedef vector<int> VI;
typedef vector<VI> VVI;
typedef vector<string> VS;
typedef pair<int,int> PII;
typedef istringstream ISS;
typedef ostringstream OSS;

#define REP( i, m, n ) for ( int i = (int)( m ); i < (int)( n ); ++i )
#define EACH( v, c ) for ( auto &v : c )

#define ITER( c ) __typeof( (c).begin() )
#define IREP( c, it ) for ( ITER(c) it = c.begin(); it != c.end(); ++it )
#define ALL( c ) (c).begin(), (c).end()

#define PB( n ) push_back( n )
#define MP( a, b ) make_pair( ( a ), ( b ) )
#define EXIST( c, e ) ( (c).find( e ) != (c).end() )

#define fst first
#define snd second

#define DUMP( x ) cerr << #x << " = " << ( x ) << endl
#define DEBUG( x ) cerr << __FILE__ << ":" << __LINE__ << ": " << #x << " = " << ( x ) << endl

struct Point
{
	double x, y;

	Point() : x( 0 ), y( 0 )
	{
		return;
	}

	Point( double x, double y ) : x( x ), y( y )
	{
		return;
	}

	Point operator + ( const Point &a ) const
	{
		return Point( x + a.x, y + a.y );
	}

	Point operator - ( const Point &a ) const
	{
		return Point( x + ( -a.x ), y + ( -a.y ) );
	}

	Point operator * ( const double &a ) const
	{
		return Point( x * a, y * a );
	}

	Point operator / ( const double &a ) const
	{
		return Point( x / a, y / a );
	}

	bool operator < ( const Point &a ) const
	{
		return x == a.x ? y < a.y : x < a.x;
	}
};

double distance( const Point &a, const Point &b )
{
	return sqrt( pow( a.x - b.x, 2. ) + pow( a.y - b.y, 2. ) );
}

double tri2cos( const double &a, const double &b, const double &c )
{
	return ( pow( b, 2. ) + pow( c, 2. ) - pow( a, 2. ) ) / ( 2 * b * c );
}

double cos2sin( const double &cos )
{
	return sqrt( abs( 1 / pow( cos, 2. ) ) );
}

void solve()
{
	Point A, B, C;

	cin >> A.x >> A.y >> B.x >> B.y >> C.x >> C.y;

	double a = distance( B, C ), b = distance( A, C ), c = distance( A, B );

	double cosA = tri2cos( a, b, c ), cosB = tri2cos( b, c, a ), cosC = tri2cos( c, a, b );
	double sinA = sqrt( abs( 1 / pow( cosA, 2. ) ) );

	double r = a / sinA;
	
	double sin2A = sin( 2 * acos( cosA ) ), sin2B = sin( 2 * acos( cosB ) ), sin2C = sin( 2 * acos( cosC ) );

	Point o = ( A * sin2A + B * sin2B + C * sin2C ) / ( sin2A + sin2B + sin2C );

	cout << o.x << ' ' << o.y << ' ' << r << endl;

	return;
}

int main()
{
	cin.tie( 0 );
	ios::sync_with_stdio( false );

	cout.precision( 3 );
	cout << fixed;

	int n;
	cin >> n;

	REP( i, 0, n )
	{
		solve();
	}

	return 0;
}

C++: #include<complex>
#include<stdio.h>
#define F(a,b,c) acos((b*b+c*c-a*a)/2/b/c)
int main(){int n;float d,e,f,g,h,i;for(scanf("%d",&n);n--;){scanf("%f%f%f%f%f%f",&d,&g,&e,&h,&f,&i);std::complex<float> a(d,g),b(e,h),c(f,i);float A=abs(b-c),B=abs(c-a),C=abs(a-b),L=F(A,B,C),s=sin(2*L),t=sin(2*F(B,C,A)),u=sin(2*F(C,A,B)),v=s+t+u;printf("%.3f %.3f %.3f\n",(d*s+e*t+f*u)/v,(g*s+h*t+i*u)/v,A/sin(L)/2);}}

C++: #include <iostream>
#include <vector>
#include <algorithm>
#include <stack>
#include <string>
#include <map>
#include <functional>
#include <cmath>
#include <cstdio>
using namespace std;

int main(){
  int n;
  cin >> n;
  for(int i = 0; i < n; i++){
    double x1, y1, x2, y2, x3, y3, x, y;
    cin >> x1 >> y1 >> x2 >> y2 >> x3 >> y3;
    x = ((y1-y3) * (y1 * y1 -y2 * y2 +x1 * x1 -x2 * x2) -(y1-y2) * (y1 * y1 -y3 * y3 +x1 * x1 -x3 * x3)) / (2 * (y1-y3) * (x1-x2)-2 * (y1-y2) * (x1-x3));
    y = ((x1-x3) * (x1 * x1 -x2 * x2 +y1 * y1 -y2 * y2) -(x1-x2) * (x1 * x1 -x3 * x3 +y1 * y1 -y3 * y3)) / (2 * (x1-x3) * (y1-y2)-2 * (x1-x2) * (y1-y3));
    double r;
    r = sqrt(pow(x - x1, 2) + pow(y - y1, 2));
    printf("%.3f %.3f %.3f\n", x, y, r);
  }
}