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<stdio.h>
#include<math.h>
#include<string>
#include<algorithm>
#include<utility>
using namespace std;
double zeti(double);
int main() {
    pair<double, double> a;
    pair<double, double> b;
    pair<double, double> c;
    pair<double, double> m1;
    pair<double, double> m2;
    double s1, s2,x1,y1,x2,y2,x,y,b1,b2;
    int n;
    scanf("%d", &n);
    for (int i = 0; i < n; ++i) {
        x = -1000.0;
        y = -1000.0;
        b1 = 0.0;
        b2 = 0.0;
        s1 = -1000.0;
        s2 = -1000.0;
        scanf("%lf%lf", &a.first, &a.second);
        scanf("%lf%lf", &b.first, &b.second);
        scanf("%lf%lf", &c.first, &c.second);
        m1.first = (a.first + b.first) / 2.0;
        m1.second = (a.second + b.second) / 2.0;
        m2.first = (b.first + c.first) / 2.0;
        m2.second = (b.second + c.second) / 2.0;
        //swap(m1.first, m1.second);
        //swap(m2.first, m2.second);
        //x is qual
        if (a.first - b.first == 0) {
            x = m1.second;
            b1 = m1.second;
            s1=0;
        }
        //y is qual
        else if (a.second - b.second == 0) {
            
            y = m1.first;
            
        }
        else {
            s1 = (a.second - b.second) / (a.first - b.first);
            s1 = 1.0 / s1*-1.0;
            b1 = m1.second - s1*m1.first;
        }
        //x is qual
        if (b.first - c.first == 0) {
            x = m2.second;
            b2 = m2.second;
            s2=0;
        }
        //y is qual
        else if (b.second - c.second == 0) {
            y = m2.first;
        }
        else {
            s2 = (c.second - b.second) / (c.first - b.first);
            s2 = 1.0 / s2*-1.0;
            b2 = m2.second - s2*m2.first;
        }
        double r,w,e;
        if(x!=-1000.0){
            if(s1==-1000.0){
                y=s2*x+b2;
            }
            else{
                y=s1*x+b2;
            }
            w = zeti(a.first - x);
            e = zeti(a.second - y);
            r = sqrt(w*w+e*e);
            printf("%.3lf %.3lf %.3lf\n", x, y,r);
            return 0;
            
        }
        if(y!=-1000.0){
            cout<<"b"<<endl;
            if(s1==-1000.0){
                x=(y-b2)/s2;
            }
            else{
                x=(y-b1)/s1;
            }
            w = zeti(a.first - x);
            e = zeti(a.second - y);
            r = sqrt(w*w+e*e);
            printf("%.3lf %.3lf %.3lf\n", x, y,r);
            return 0;
        }
        if (x == -1000.0) {
            x = (b1 - b2) / (s2 - s1);
        }
        if (y==-1000.0) {
            y = s2*x + b2;
        }
        
        
        w = zeti(a.first - x);
        e = zeti(a.second - y);
        r = sqrt(w*w+e*e);
        printf("%.3lf %.3lf %.3lf\n", x, y,r);
        
    }
    return 0;
}
double zeti(double center) {
    if (center < 0) {
        center *= -1;
    }
    return center;
}

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

using namespace std;

int main() {
    int n, a, b, c, d, e, f;
    double x1, x2, x3, y1, y2, y3, px, py, r;
    cin >> n;
    while (n--) {
        cin >> x1 >> x2 >> x3 >> y1 >> y2 >> y3;
        a = 2 * (x1 - x2);
        b = 2 * (y1 - y2);
        c = x1*x1 + y1*y1 - x2*x2 - y2*y2;
        d = 2 * (x1 - x3);
        e = 2 * (y1 - y3);
        f = x1*x1 + y1*y1 - x3*x3 - y3*y3;
        px = (c*e - b*f) / (a*e - b*d);
        py = (c*d - a*f) / (b*d - a*e);
        r = sqrt(pow(px - x1, 2) + pow(py - y1, 2));
        printf("%.3f %.3f %.3f\n", px, py, r);
    }
    
    return 0;
}