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 <complex>
#include <cstdio>
#include <cmath>
using namespace std;

// ?????§?¨?????????¨??????
typedef complex<double> P;
// ???????????
#define PI 3.1415926535898

// ?¨±?????????????????
#define EPS (1e-10)
//XY??§?¨?
#define X real()
#define Y imag()

// ????§???¢?????????
class Triangle{

private:
	//????§???¢??????????????§?¨?
	P a, b, c;
	//????§???¢??????????????????
	double edgeA,edgeB,edgeC;
	//????§???¢???????§??????§??????(????????¢???)
	double angleA,angleB,angleC;
	//????????????????????????????§????????±?????????¢??°
	double LawOfCosines(double a,double b, double c){
		return acos( (b*b+c*c-a*a) / (2.0*b*c) );
	}


public:
	//?????????????????????(??????????????¨?????¨?§????????????????)
	Triangle(P p1, P p2, P p3){
		a = p1;
		b = p2;
		c = p3;
		edgeB = abs(c-a);
		edgeA = abs(b-c);
		edgeC = abs(a-b);
		angleA = LawOfCosines(edgeA,edgeB,edgeC);
		angleB = LawOfCosines(edgeB,edgeC,edgeA);
		angleC = LawOfCosines(edgeC,edgeA,edgeB);
	}

	double circumscribedCircleRadius(){//?????\?????????????????????
		return ( edgeA / sin(angleA) / 2.0 );
	}
	double circumscribedCircleX(){//??????(?????\????????????)???X??§?¨??????????
		double A = sin(2.0*angleA);
		double B = sin(2.0*angleB);
		double C = sin(2.0*angleC);
		return ( (a.X * A + b.X * B + c.X * C) / (A+B+C) );
	}
	double circumscribedCircleY(){//??????(?????\????????????)???Y??§?¨??????????
		double A = sin(2.0*angleA);
		double B = sin(2.0*angleB);
		double C = sin(2.0*angleC);
		return ( (a.Y * A + b.Y * B + c.Y * C) / (A+B+C) );
	}
};

int main(){
	int n;
	double x1, x2, x3, y1, y2, y3;
	double r, xp, yp;

	scanf("%d", &n);
	for (int i=0 ; i<n ; i++){
		scanf("%lf %lf %lf %lf %lf %lf", &x1, &y1, &x2, &y2, &x3, &y3);
		P a( x1 , y1 );
		P b( x2 , y2 );
		P c( x3 , y3 );
		Triangle Tr(a,b,c);
		r  = Tr.circumscribedCircleRadius();
		xp = Tr.circumscribedCircleX();
		yp = Tr.circumscribedCircleY();
		printf("%.3f %.3f %.3f\n", xp,yp,r);
	}
}

C++: #include <iostream>
#include <iomanip>
#include <cmath>
using namespace std;

inline double square(double x){return x*x;}
inline double Roundoff(double x){
	if( x<0 ){
		x*=-1;
		x=(x-(x-int(x*1000)/1000))+(((x*1000)-int(x*1000))*10)>=4?0.001:0;
		x*=-1;
	}else{
		x=(x-(x-int(x*1000)/1000))+(((x*1000)-int(x*1000))*10)>=4?0.001:0;
	}
	return x;
}

void SolveSimultEq(double &x,double &y,double a,double b,double c,double d,double e,double f);
int main(){
	int datanum;
	double *x1,*y1,*x2,*y2,*x3,*y3;
	cin>>datanum;
	x1=new double[datanum];
	y1=new double[datanum];
	x2=new double[datanum];
	y2=new double[datanum];
	x3=new double[datanum];
	y3=new double[datanum];
	
	for( int i=0;i<datanum;i++ ){
		cin>>x1[i]>>y1[i]>>x2[i]>>y2[i]>>x3[i]>>y3[i];
	}
	for( int i=0;i<datanum;i++ ){
		double px,py,r;
		
		SolveSimultEq(px,py,2*(x1[i]-x2[i]),2*(y1[i]-y2[i]),square(x1[i])-square(x2[i])+square(y1[i])-square(y2[i]),
  			  	    2*(x2[i]-x3[i]),2*(y2[i]-y3[i]),square(x2[i])-square(x3[i])+square(y2[i])-square(y3[i]));
		r=sqrt(square(x1[i]-px)+square(y1[i]-py));
		cout<<fixed<<setprecision(3)<<px<<" "<<setprecision(3)<<py<<" "<<setprecision(3)<<r<<endl;

	}

	delete x1;
	delete y1;
	delete x2;
	delete y2;
	delete x3;
	delete y3;
	return 0;
}

void SolveSimultEq(double &x,double &y,double a,double b,double c,double d,double e,double f){
	double delta=a*e-b*d;
	
	x=(c*e-b*f)/delta;
	y=(a*f-c*d)/delta;
}

C++: #include <iostream>
#include <cmath>
using namespace std;

int main() {
  int n;
  double x1, y1, x2, y2, x3, y3;
  double a1, b1, c1, a2, b2, c2;
  double x, y, r;
  cin >> n;
  while (n--) {
    cin >> x1 >> y1 >> x2 >> y2 >> x3 >> y3;
    a1 = x2-x1;
    b1 = y2-y1;
    c1 = -a1*(x1+x2)*0.5 - b1*(y1+y2)*0.5;
    
    a2 = x3-x2;
    b2 = y3-y2;
    c2 = -a2*(x2+x3)*0.5 - b2*(y2+y3)*0.5;

    y = (a2*c1-a1*c2)/(a1*b2-a2*b1);
    if (a1) {
      x = -(b1*y+c1)/a1;
    } else {
      x = -(b2*y+c2)/a2;
    }
    r = sqrt((x1-x)*(x1-x) + (y1-y)*(y1-y));

    cout.setf(ios::fixed);
    cout.precision(3);
    cout << x << " " << y << " " << r << endl;
  }
}

C++: #include<iostream>
#include<cmath>
int main(){float a,b,c,d,e,f,g,h,i,j,k,l,n,s;for(std::cin>>n;n--;)std::cin>>g>>h>>i>>j>>k>>l,a=i-k,d=j-l,b=k-g,e=l-h,c=g-i,f=h-j,a=sqrt(d=d*d+a*a),b=sqrt(e=e*e+b*b),c=sqrt(f=f*f+c*c),s=(a+b+c)/2,s=sqrt(s*(s-a)*(s-b)*(s-c)),s*=s*16,a=d*(e+f-d),b=e*(f+d-e),c=f*(d+e-f),g-=d=(a*g+b*i+c*k)/s,h-=e=(a*h+b*j+c*l)/s,printf("%.3f %.3f %.3f\n",d,e,sqrt(g*g+h*h));}