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 <cstdio>
#include <cstring>
#include <algorithm>
#include <string>
#include <cmath>

using namespace std;

int main()
{
	int n;
	scanf("%d", &n);
	for (int i = 0; i < n; ++i)
	{
		double x[3], y[3];
		for (int j = 0; j < 3; ++j)
			scanf("%lf %lf", x+j, y+j);
		
		double a[2], b[2];
		for (int j = 0, c = 0; j < 3 && c < 2; ++j)
		{
			for (int k = j+1; k < 3 && c < 2; ++k)
			{
				if (y[j] == y[k])
					continue;

				a[c] = -(x[k]-x[j])/(y[k]-y[j]);
				b[c] = (y[k]+y[j] - (x[k]+x[j])*a[c])/2;
				++c;
			}
		}
		double px = (b[0]-b[1])/(a[1]-a[0]);
		double py = a[0] * px + b[0];
		double r = sqrt((px-x[0])*(px-x[0])+(py-y[0])*(py-y[0]));
		printf("%.3f %.3f %.3f\n", px, py, r);
	}

	return 0;
}

C++: #include<stdio.h>
#include<math.h>
#define P(x) pow(double(x),2)



int main(){


	int i,j,k;
	int n;
	double x[3],y[3];
	double xp,yp,r;
	double a1,a2,b1,b2,c1,c2;
	
	while((scanf("%d",&n))!=EOF){
		for(i=0;i<3;i++){
			scanf("%lf",&x[i]);
			scanf("%lf",&y[i]);
		}
		a1=2*(x[1]-x[0]);
		a2=2*(x[2]-x[1]);
		b1=2*(y[1]-y[0]);
		b2=2*(y[2]-y[1]);
		c1=(P(x[0])-P(x[1])+P(y[0])-P(y[1]));
		c2=(P(x[1])-P(x[2])+P(y[1])-P(y[2]));
	
		xp=(b1*c2-b2*c1)/(a1*b2-a2*b1);
		yp=(c1*a2-c2*a1)/(a1*b2-a2*b1);
		r=(double)(sqrt((long double)(((xp-x[0])*(xp-x[0]))+((yp-y[0])*(yp-y[0])))));	


		printf("%.3f %.3f %.3f\n",xp,yp,r);

	}



}

C++: #include <iostream>
#include <algorithm>
#include <cstdio>
#include <cmath>
#include <string>
#include <cctype>
#include <stack>
#include <queue>
#include <vector>
#include <cstdlib>
#include <list>
#define _USE_MATH_DEFINES
#include <math.h>

using namespace std;

int main() {

	int n;
	double x1, x2, x3, y1, y2, y3;
	double X, Y, R;
	double a, b, c, d, e, f;

	cin >> n;

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

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

		Y = (a*b + c*d) / (e - f);
		X = (b+2*Y*(y1-y2))/(-2*c);
		R = sqrt((X - x1)*(X - x1) + (Y-y1)*(Y-y1));

		if (X > 0)
			X = (int)(X * 1000 + 0.5) ;
		else X = (int)(X * 1000 - 0.5) ;

		if (Y>0)
			Y = (int)(Y * 1000 + 0.5) ;
		else Y = (int)(Y * 1000 - 0.5) ;

		if (R > 0)
			R = (int)(R * 1000 + 0.5);
		else R = (int)(R * 1000 - 0.5);

		printf("%.3f %.3f %.3f\n", X/1000, Y/1000, R/1000);
	}


	return 0;
}

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

int main() {
	int sampleNum;
	scanf("%d", &sampleNum);
	for (; sampleNum > 0; --sampleNum) {
		double x1, y1, x2, y2, x3, y3;
		scanf("%lf %lf %lf %lf %lf %lf", &x1, &y1, &x2, &y2, &x3, &y3);

		double ax = x2 - x1;
		double ay = y2 - y1;
		double a = sqrt(ax * ax + ay * ay);
		double bx = x3 - x1;
		double by = y3 - y1;
		double b = sqrt(bx * bx + by * by);
		double cx = x3 - x2;
		double cy = y3 - y2;
		double c = sqrt(cx * cx + cy * cy);

		double crossabz = ax * by - ay * bx;
		double crossbcz = bx * cy - by * cx;
		double crosscaz = cx * ay - cy * ax;

		double sinA = crossbcz / (b * c);
		double sinB = crosscaz / (c * a);
		double sinC = crossabz / (a * b);
		double sin2A = sin(2.*asin(sinA));
		double sin2B = sin(2.*asin(sinB));
		double sin2C = sin(2.*asin(sinC));
		double px = (sin2A * x1 + sin2B * x2 + sin2C * x3) / (sin2A + sin2B + sin2C);
		double py = (sin2A * y1 + sin2B * y2 + sin2C * y3) / (sin2A + sin2B + sin2C);

		double s = fabs(crossabz) / 2.;
		double r = a * b * c / (4. * s);

		printf("%.3lf %.3lf %.3lf\n", px, py, r);
	}
	return 0;
}