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<bits/stdc++.h>
#include<vector>
#include<list>
#include<stack>
#include<queue>
#include<algorithm>
#include<complex>
#include<cmath>
using namespace std;

#define PI 3.1415926535898

//?????§?¨?????????¨??????
typedef complex<double> P;


//?¨±?????????
#define EPS (1e-10)
//X Y??§?¨?
#define X real()
#define Y imag()

class Triangle {
    private:
    //????§???¢???3????????§?¨?
    P a,b,c;
    //????§???¢???????????????
    double edgeA, edgeB, edgeC;
    //????§???¢????§??????§??????
    double angleA, angleB, angleC;
    //??????????????????3???????§????????±???????
    double LawOfCosines ( double a, double b, double c) {
        return acos((b*b+c*c+a*a)/(2.0*b*c));
    }
    //2??????double??????????????????
    bool equal (double a,double b) {
        return (abs(a-b)<EPS)?true:false;
    }

    public:
    //?????????????????????
    Triangle(P p1, P p2, P p3) {
        a=p1;
        b=p2;
        c=p3;
        edgeB=abs(c-a);
        edgeA=abs(b-c);
        edgeC=abs(a-b);
        angleA=LawOfCosines(edgeA, edgeB, edgeC);
        angleB=LawOfCosines(edgeB, edgeC, edgeA);
        angleC=LawOfCosines(edgeC, edgeA, edgeB);
    }

    double circumscribedCircleRadius() {//?????\????????????
        return (edgeA/sin(angleA)/2.0);
    }

    double circumscribedCircleX() {//?????\????????????X??§?¨?
        double A=sin(2.0*angleA);
        double B=sin(2.0*angleB);
        double C=sin(2.0*angleC);
        return ((a.X * A + b.X * B + c.X * C)/(A+B+C));
    }

    double circumscribedCircleY() {//?????\????????????Y??§?¨?
        double A=sin(2.0*angleA);
        double B=sin(2.0*angleB);
        double C=sin(2.0*angleC);
        return ((a.Y * A + b.Y * B + c.Y * C)/(A+B+C));
    }
};


int main(){
    int mod=1000000007;
    int n;
    scanf("%d",&n);
    for (int i=0;i<n;i++) {
        double x1,y1,x2,y2,x3,y3;
        double r,xp,yp;
        scanf("%f %f %f %f %f %f",&x1,&y1,&x2,&y2,&x3,&y3);
        P a (x1,y1);
        P b (x2,y2);
        P c (x3,y3);
        Triangle Tr(a,b,c);
        xp=Tr.circumscribedCircleX();
        yp=Tr.circumscribedCircleY();
        r=Tr.circumscribedCircleRadius();

        printf("%.10f %.10f %.10f\n",xp,yp,r);
    }

    return 0;
}

C++: #include<stdio.h>
#include<math.h>
int main(){
	int a;
	scanf("%d",&a);
	while(a--){
		double x1,y1,x2,y2,x3,y3;
		scanf("%lf%lf%lf%lf%lf%lf",&x1,&y1,&x2,&y2,&x3,&y3);
		double a1=2*(x2-x1);
		double b1=2*(y2-y2);
		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);
	}
}