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<stdio.h>
#include<iostream>
#include<math.h>
using namespace std;
int main(){
    int a;
    cin >> a;
    while(a--){
        double x1,y1,x2,y2,x3,y3;
        cin >> x1 >>y1 >>x2 >> y2 >> x3 >> y3;
        double a1,a2,b1,b2,c1,c2,x,y,r;
         a1=2*(x2-x1);
         b1=2*(y2-y1);
         c1=x1*x1-x2*x2+y1*y1-y2*y2;
         a2=2*(x3-x1);
         b2=2*(y3-y1);
         c2=x1*x1-x3*x3+y1*y1-y3*y3;
         x=(b1*c2-b2*c1)/(a1*b2-a2*b1);
         y=(c1*a2-c2*a1)/(a1*b2-a2*b1);
         r=hypot(x-x1,y-y1);
        printf("%.3lf %.3lf %.3lf\n",x,y,r);
    }
}

C++: //Circumscribed Circle of a Triangle
#include<bits/stdc++.h>
using namespace std;

int main(){
  int n;
  scanf("%d", &n);
  for(int i=0; i<n; i++){
    double x1, y1, x2, y2, x3, y3;
    double px, py, r;
    scanf("%lf %lf %lf %lf %lf %lf", &x1, &y1, &x2, &y2, &x3, &y3);
    px=((y1-y2)*(y2-y3)*(y3-y1)+(y1-y2)*(x2+x3)*(x2-x3)+(y3-y2)*(x1+x2)*(x1-x2))/(2*((y1-y2)*(x2-x3)+(y3-y2)*(x1-x2)));
    py=((x1-x2)*(x2-x3)*(x3-x1)+(x1-x2)*(y2+y3)*(y2-y3)+(x3-x2)*(y1+y2)*(y1-y2))/(2*((x1-x2)*(y2-y3)+(x3-x2)*(y1-y2)));
    r=sqrt(pow(x1-px, 2.0)+pow(y1-py, 2.0));
    printf("%.3f %.3f %.3f\n", px, py, r);
  }
  return 0;
}

C++: #include<complex>
#include<stdio.h>
#include<cmath>
#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("%lf%lf%lf%lf%lf%lf",&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),
		s=sin(2*F(A,B,C)),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(F(A,B,C))/2);
	}
}

C++: #include<iostream>
#include<cstdio>
#include<math.h>
using namespace std;

int main()
{
	int i,n,flg;
	double x1,x2,x3,y1,y2,y3;
	double m1,m2,xm1,xm2,ym1,ym2,xo,yo,r;
	//m1,m2…辺の法線 xm1,ym1…辺の中点の座標

	cin>>n;
	for(i=0;i<n;i++){
		flg=0;
		cin>>x1>>y1>>x2>>y2>>x3>>y3;

		xm1=(x1+x2)/2;
		xm2=(x2+x3)/2;
		ym1=(y1+y2)/2;
		ym2=(y2+y3)/2;
		
		if(y1-y2!=0) 		m1=(-1)*(x1-x2)/(y1-y2);
		else if(y1-y2==0)	flg=1;
		
		if(y2-y3!=0)		m2=(-1)*(x2-x3)/(y2-y3);
		else if(y2-y3==0)	flg=2;
		
		if(flg==0) 	xo=(m1*xm1-m2*xm2+ym2-ym1)/(m1-m2);
		else if(flg==1)xo=xm1;
		else if(flg==2)xo=xm2;

		if(flg==1)yo=m2*(xo-xm2)+ym2;
		else		yo=m1*(xo-xm1)+ym1;
		r=sqrt((x1-xo)*(x1-xo)+(y1-yo)*(y1-yo));
		printf("%.3lf %.3lf %.3lf \n",xo,yo,r);
	}
}