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 <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));
    cout << x << " " << y << " ";
    printf("%.3f\n", r);
  }
}

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

C++: #include <stdio.h>
#include <math.h>

using namespace std;


int main(){
	int n;
	double x1,x2,x3,y1,y2,y3,ox,oy,r;
	scanf("%d",&n);

	for(int i=0;i<n;i++){
		scanf("%lf %lf %lf %lf %lf %lf",&x1,&y1,&x2,&y2,&x3,&y3);
		ox=((y2-y1)*((y3*y3-y1*y1)+(x3*x3-x1*x1))-(y3-y1)*((y2*y2-y1*y1)+(x2*x2-x1*x1)))/
				(2*((x3-x1)*(y2-y1)-(x2-x1)*(y3-y1)));
		if(y2 != y1){
			oy=(2*(x1-x2)*ox+(y2*y2-y1*y1)+(x2*x2-x1*x1))/(2*(y2-y1));
		}else{
			oy=(2*(x1-x3)*ox+(y3*y3-y1*y1)+(x3*x3-x1*x1))/(2*(y3-y1));
		}

		r = sqrt((ox-x1)*(ox-x1)+(oy-y1)*(oy-y1));
		printf("%.3lf %.3lf %.3lf\n",ox,oy,r);
	}
    return 0;
}

C++: #include<iostream>
#include<cstdio>
#include<cmath>
#include<string>
#include<algorithm>
using namespace std;
#define int long long

signed main(){

        int n;
        scanf("%lld",&n);
        for(int i=0;i<n;i++){
                double x1,x2,x3,y1,y2,y3;
                scanf("%lf %lf %lf %lf %lf %lf", &x1, &y1, &x2, &y2, &x3, &y3);
                double t1 = atan2(x2-x1,y2-y1);
                double t2 = atan2(x3-x1,y3-y1);
                double d = sqrt((x3-x2)*(x3-x2)+(y3-y2)*(y3-y2));
                double r = d/sin(abs(t1-t2))/2;
                double d2 = sqrt(r*r-d*d/4);
                double xc = (x3+x2)/2 - (y3-y2)/d*d2;
                double yc = (y3+y2)/2 + (x3-x2)/d*d2;
                printf("%.3f %.3f %.3f\n", xc,yc, r);

        }

        return 0;
}

C++: #include <iostream>
#include <cmath>
#include <algorithm>
#include <string>
#include <stdio.h>
using namespace std;
int main(){
    int n;
    cin >> n;
    for(int i=0;i<n;i++){
    double x1,y1,x2,y2,x3,y3;
    cin >> x1 >> y1 >> x2 >> y2 >> x3 >> y3;
    double x,y,r1,r2,r3;
    double a,b,c,d,e,f;
    a=2*x1-2*x2;
    b=2*y1-2*y2;
    c=x1*x1-x2*x2+y1*y1-y2*y2;
    d=2*x2-2*x3;
    e=2*y2-2*y3;
    f=x2*x2-x3*x3+y2*y2-y3*y3;
    y=(a*f-c*d)/(a*e-b*d);
    x=(c-b*y)/a;
    r1=sqrt((x1-x)*(x1-x)+(y1-y)*(y1-y));
        r2=sqrt((x2-x)*(x2-x)+(y2-y)*(y2-y));
        r3=sqrt((x3-x)*(x3-x)+(y3-y)*(y3-y));
    
    printf("%.3f %.3f %.3f\n",x,y,r1);
}
}