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 <sstream>
#include <string>
#include <vector>
#include <map>
#include <algorithm>
#include <iostream>
#include <utility>
#include <set>
#include <cctype>
#include <queue>
#include <stack>
#include <cstdio>
#include <cstdlib>
#include <cmath>
using namespace std;
#define eps 1e-8
int main(void) {
    int n;
    cin >> n;
    for (int i = 0; i < n; i++) {
        double x1, x2, y1, y2, a, b, c, d, e, f;
        cin >> a >> b >> c >> d >> e >> f;
        x1 = c - a; y1 = d - b;
        x2 = e - a; y2 = f - b;
        double x = (y1 * (x2 * x2 + y2 * y2) - y2 * (x1 * x1 + y1 * y1)) / (2 * (y1 * x2 - x1 * y2));
        double y, r;
        if (-eps < y1 && y1 < eps) y = y2 / 2 - (x2 / y2) * (x - x2 / 2);
        else y = y1 / 2 - (x1 / y1) * (x - x1 / 2);
        r = sqrt(x * x + y * y);
//        printf("%.5f\n", r);
        x += a; y += b;
        int intx = x * 10000;
        int inty = y * 10000;
        int intr = r * 10000;
        if (intx % 10 >= 5) x = (intx + 5) / 10000.0;
        if (inty % 10 >= 5) y = (inty + 5) / 10000.0;
        if (intr % 10 >= 5) r = (intr + 5) / 10000.0;
        printf("%.3f %.3f %.3f\n", x, y, r);
    }
    return 0;
}

C++: #include <cstdio>
#include <cstdlib>
#include <iostream>
#include <algorithm>
#include <cstring>
#include <string.h>
#include <bitset>
#include <queue>
#include <map>
#include <string>
#include <stack>
#include <utility>
#include <queue>
#include <cmath>
#define mp make_pair
#define pii pair<long long int,long long int> 
#define ff first
#define pb push_back
#define ss second
#define ll long long 
#define ull unsigned long long
#define vi vector<long long int>
#define vii vector<pii>
#define vvi vector <vi>
#define rep(x,a,b,c) for(int x=a;x<=b;x+=c)
#define repp(x,a,b) rep(x,a,b,1)
#define rev(x,a,b,c) for(int x=a;x>=b;x-=c)
#define revv(x,a,b) rev(x,a,b,1)
#define OO (int)2e9
#define INF (ll)1e18
 
using namespace std;

double a,b,c,d,xx,yy,x2,y2,x3,y3;
int tc;

double xc()
{
	return ((xx*xx+yy*yy)*(y2-y3)+(x2*x2+y2*y2)*(y3-yy)+(x3*x3+y3*y3)*(yy-y2))/(double)d;
}

double yc()
{
	return ((xx*xx+yy*yy)*(x3-x2)+(x2*x2+y2*y2)*(xx-x3)+(x3*x3+y3*y3)*(x2-xx))/(double)d;
}

double rads()
{
	return (b+c-a)/(double)2;
}

double findabc()
{
	a=sqrt((abs(x2-xx))*(abs(x2-xx))+(abs(y2-yy))*(abs(y2-yy)));
	b=sqrt((abs(x3-x2))*(abs(x3-x2))+(abs(y3-y2))*(abs(y3-y2)));
	c=sqrt((abs(x3-xx))*(abs(x3-xx))+(abs(y3-yy))*(abs(y3-yy)));
	d=2*(xx*(y2-y3)+x2*(y3-yy)+x3*(yy-y2));
}

int main()
{
	scanf("%d",&tc);
	while(tc--)
	{
		scanf("%lf %lf %lf %lf %lf %lf",&xx,&yy,&x2,&y2,&x3,&y3);
		findabc();
		//printf("%.3lf %.3lf %.3lf",a,b,c);
		printf("%.3lf %.3lf %.3lf\n",xc(),yc(),rads());
	}
	return 0;
}

C++: #include <bits/stdc++.h>

using namespace std;

#define LOG(...) fprintf(stderr, __VA_ARGS__)
//#define LOG(...)
#define FOR(i, a, b) for(int i=(int)(a); i<(int)(b); ++i)
#define REP(i, n) for(int i=0; i<(int)(n); ++i)
#define ALL(a) (a).begin(), (a).end()
#define RALL(a) (a).rbegin(), (a).rend()
#define EXIST(s, e) ((s).find(e)!=(s).end())
#define SORT(c) sort(ALL(c))
#define RSORT(c) sort(RALL(c))
#define SQ(n) (n) * (n)

typedef long long ll;
typedef unsigned long long ull;
typedef vector<bool> vb;
typedef vector<int> vi;
typedef vector<ll> vll;
typedef vector<vb> vvb;
typedef vector<vi> vvi;
typedef vector<vll> vvll;
typedef pair<int, int> pii;
typedef pair<ll, ll> pll;

int main() {
  int n;
  float x1, y1, x2, y2, x3, y3;
  cin >> n;
  REP(i, n){
    cin >> x1 >> y1 >> x2 >> y2 >> x3 >> y3;
    float a = 2 * (x2 - x1);
    float b = 2 * (y2 - y1);
    float e = x2 * x2 + y2 * y2 - x1 * x1 - y1 * y1;
    float c = 2 * (x3 - x2);
    float d = 2 * (y3 - y2);
    float f = x3 * x3 + y3 * y3 - x2 * x2 - y2 * y2;

    float D = 1 / (a * d - b * c);
    float A = (d * e - b * f) * D;
    float B = (-c * e + a * f) * D;
    printf("%.3f %.3f %.3f\n", A, B, sqrt(SQ(x1-A)+SQ(x1-B)));
  }
}

C++: #include <iostream>

using namespace std;

int n;
double x[4],y[4],r;

int main(){
    cin >> n;
	while(n--){
		for(int i=0;i<3;i++){
			cin >> x[i] >> y[i];
		}
		x[3]=((y[2]-y[1])*(x[1]-x[0])*(x[2]-x[0])-(y[1]-y[0])*(x[1]+x[0])*(x[2]-x[0])+(y[2]-y[0])*(x[1]-x[0])*(x[2]+x[0]))/(2*(y[2]-y[0])*(x[1]-x[0])-(y[1]-y[0])*(x[2]-x[0]));
		y[3]=(y[0]+y[1])/2-(y[1]-y[0])*(x[3]-(x[0]+x[1])/2)/(x[1]-x[0]);
		printf("%.3lf %.3lf\n",x[3],y[3]);
	}
	return 0;
}