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 <climits>
#include <string>
#include <vector>
#include <stack>
#include <queue>
#include <set>
#include <map>
#include <algorithm>
#include <functional>

using namespace std;

typedef vector<int> VI;
typedef vector<VI> VVI;
typedef vector<string> VS;
typedef pair<int,int> PII;
typedef long long ll;
typedef unsigned long long ull;

#define REP( i, m, n ) for ( int i = (int)( m ); i < (int)( n ); i++ )
#define UREP( i, m, n ) for ( unsigned int i = (unsigned int)( m ); i < (unsigned int)( n ); i++ )

#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 RALL( c ) (c).rbegin(), (c).rend()

#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

double sqdist( double x1, double y1, double x2, double y2 )
{
	return pow( x1 - x2, 2 ) + pow( y1 - y2, 2 );
}

double dist( double x1, double y1, double x2, double y2 )
{
	return sqrt( sqdist( x1, y1, x2, y2 ) );
}

int main()
{
	int n;
	cin >> n;

	REP( dn, 0, n )
	{
		double x1, y1, x2, y2, x3, y3;
		cin >> x1 >> y1 >> x2 >> y2 >> x3 >> y3;

		double mx = ( x1 + x2 ) / 2, my = ( y1 + y2 ) / 2;
		double a = -( ( x2 - x1 ) / ( y2 - y1 ) );
		double th = atan( a );

		double low = -100.0, high = 100.0, mid = 0;

		REP( i, 0, 1000 )
		{
			mid = ( low + high ) / 2;
			double cx = mx + cos( th ) * mid, cy = my + sin( th ) * mid;

			double d1 = sqdist( x1, y1, cx, cy ), d2 = sqdist( cx, cy, x3, y3 );

			if ( d1 < d2 )
			{
				high = mid;
			}
			else if ( d2 < d1 )
			{
				low = mid;
			}
		}

		double rx = mx + cos( th ) * mid, ry = my + sin( th ) * mid;

		cout.precision( 4 );
		cout << setiosflags( ios::showpoint ) << rx << ' ' << ry << ' ' << dist( x1, y1, rx, ry ) << endl;
	}

	return 0;
}

C++: #include <iostream>
#include <cstdio>
#include <stdio.h>
#include <math.h>
using namespace std;
int main(){
	int n;
	cin>>n;
	for(int i=0;i<n;i++){
		double x1,y1,x2,y2,x3,y3,xp,yp,r;
		cin>>x1>>y1>>x2>>y2>>x3>>y3;
		xp=0;
		yp=0;
		double a=y2-y1,b=y3-y1,c=y2-y3,d=x2-x1,e=x3-x1;
		if(y1 != y2 && y1 != y3){
			xp=(c/2-e*(x1+x3)/2/b-d*(x2+x1)/2/a)/(-e/b+d/a);
			yp=-e/b*(xp-(x1+x3)/2)+(y1+y3)/2;
		}else if(y1==y2){
			xp=(x1+x2)/2;
			yp=-e/b*(xp-(x1+x3)/2)+(y1+y3)/2;
		}else if(y1==y3){
			xp=(x1+x3)/2;
			yp=-d/a*(xp-(x1+x2)/2)+(y1+y2)/2;
		}
		r = sqrt((x1-xp)*(x1-xp)+(y1-yp)*(y1-yp));
		xp*=1000;
		if(xp>0)
			xp+=0.5;
		else
			xp-=0.5;
		int xp2=xp;
		yp*=1000;
		if(yp>0)
			yp+=0.5;
		else
			yp-=0.5;
		int yp2=yp;
		printf("%.3lf %.3lf %.3lf\n",xp2/(double)1000,yp2/(double)1000,r);
	}
	return 0;
}

C++: #include <bits/stdc++.h>  
 
using namespace std;
 
#define FOR(i, j, k) for(int i = j; i < k; ++i)
#define rep(i, j) FOR(i, 0, j)
#define repr(i, j) for(int i = j; i >= 0; --i)
#define INF (1 << 30)
 
typedef long long ll;
typedef unsigned long long ull;
typedef pair<int, int> P;

int main() {
	int N;
	scanf("%d", &N);
	rep(i, N) {
		double x1, y1, x2, y2, x3, y3;
		scanf("%lf %lf %lf %lf %lf %lf", &x1, &y1, &x2, &y2, &x3, &y3);     
		double a = 2 * (x2 - x1);
	    double b = 2 * (y2 - y1);
	    double c = x1 * x1 - x2 * x2 + y1 * y1 - y2 * y2;
	    double d = 2 * (x3 - x2);
	    double e = 2 * (y3 - y2);
	    double f = x2 * x2 - x3 * x3 + y2 * y2 - y3 * y3;
	          
	    double p = (b * f - c * e)/(a * e - d * b);
	    double q = (a * f - c * d)/(b * d - a * e);
		double r1 = sqrt( pow( p - x1, 2 ) + pow( q - y1, 2 ) );
        double r2 = sqrt( pow( p - x2, 2 ) + pow( q - y2, 2 ) );
        double r3 = sqrt( pow( p - x3, 2 ) + pow( q - y3, 2 ) );
        double r = ( r1 + r2 + r3 ) / 3.0;
		printf("%.3f %.3f %.3f\n", p, q, r);
	}
	return 0;
}