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, x2, rx, ry ) << endl;
	}

	return 0;
}

C++: #include <iostream>
#include <cstdio>
#include <cmath>
using namespace std;
#define x1 0
#define y1 1
#define x2 2
#define y2 3
#define x3 4
#define y3 5

int main()
{
	int n;
	double xy[6],a,b,c,d,e,f,x,y,r;

	cin>>n;
	for(int i=0;i<n;i++)
	{
		for(int j=0;j<6;j++)
			cin>>xy[j];

		a=2*(xy[x2]-xy[x1]);
		b=2*(xy[y2]-xy[y1]);
		c=2*(xy[x3]-xy[x2]);
		d=2*(xy[y3]-xy[y2]);
		e=xy[y2]*xy[y2]-xy[y1]*xy[y1]+xy[x2]*xy[x2]-xy[x1]*xy[x1];
		f=xy[y3]*xy[y3]-xy[y2]*xy[y2]+xy[x3]*xy[x3]-xy[x2]*xy[x2];

		x=(d*e-b*f)/(a*d-b*c);
		y=(a*f-c*e)/(a*d-b*c);
		r=sqrt((xy[x1]-x)*(xy[x1]-x)+(xy[y1]-y)*(xy[y1]-y));

		if(x<0)
			x-=0.0005;
		else x+=0.0005;
		if(y<0)
			y-=0.0005;
		else y+=0.0005;
		r+=0.0005;

		printf("%.3lf %.3lf %.3lf\n",x,y,r);
	}
}

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

using namespace std;

int main(void)
{
    int n;
    cin >> n;
    for(int i=0;i<n;i++){
        double x1,x2,x3;
        double y1,y2,y3;
        cin 
            >> x1 >> y1
            >> x2 >> y2
            >> x3 >> y3;
        double l12 = sqrt((x1-x2)*(x1-x2)+(y1-y2)*(y1-y2));
        double l23 = sqrt((x2-x3)*(x2-x3)+(y2-y3)*(y2-y3));
        double l31 = sqrt((x3-x1)*(x3-x1)+(y3-y1)*(y3-y1));
        double cos123 = (l12*l12 + l23*l23 - l31*l31)/(2.0*l12*l23);
        double sin123 = sqrt(1.0-cos123*cos123);
        double r = l31 / (2.0*sin123);
        double coeff[4];
        double a = l23 * l23; // 1
        double b = l31 * l31; // 2
        double c = l12 * l12; // 3
        coeff[0] = a * ( b + c - a );
        coeff[1] = b * ( c + a - b );
        coeff[2] = c * ( a + b - c );
        coeff[3] = coeff[0] + coeff[1] + coeff[2];
        double xc = (coeff[0]*x1+coeff[1]*x2+coeff[2]*x3)/coeff[3];
        double yc = (coeff[0]*y1+coeff[1]*y2+coeff[2]*y3)/coeff[3];
#define sishagonyu(x) round(x*1000.0)/1000.0
        xc = sishagonyu(xc);
        yc = sishagonyu(yc);
        r  = sishagonyu(r);
        printf("%1.3f %1.3f %1.3f\n",
                xc,yc,r);
    }

    return 0;
}