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))
	}
}

Python: def solve():
    from sys import stdin
    f_i = stdin
    
    n = int(f_i.readline())
    for i in range(n):
        x1, y1, x2, y2, x3, y3 = map(float, f_i.readline().split())
        A = x1 + y1 * 1j
        B = x2 + y2 * 1j
        C = x3 + y3 * 1j
        a = abs(C - B)
        b = abs(A - C)
        c = abs(B - A)
        c1 = a**2 * (b**2 + c**2 - a**2)
        c2 = b**2 * (c**2 + a**2 - b**2)
        c3 = c**2 * (a**2 + b**2 - c**2)
        
        U = (c1 * A + c2 * B + c3 * C) / (c1 + c2 + c3)
        R = abs(U - A)
        
        print('{:.3f} {:.3f} {:.3f}'.format(U.real, U.imag, R))

solve()

Python: import sys,math
if sys.version_info[0]>=3: raw_input=input
N=int(raw_input())
for i in range(N):
	x1,y1,x2,y2,x3,y3=[float(e) for e in raw_input().split()]
	a1=2*x2-2*x1
	b1=2*y2-2*y1
	c1=x1*x1-x2*x2+y1*y1-y2*y2
	a2=2*x3-2*x1
	b2=2*y3-2*y1
	c2=x1*x1-x3*x3+y1*y1-y3*y3
	x=(b1*c2-b2*c1)/(a1*b2-a2*b1)
	y=(c1*a2-c2*a1)/(a1*b2-a2*b1)
	print('%.3f %.3f %.3f'%(x,y,math.hypot(x1-x,y1-y)))

Python: # coding=utf-8
import math


if __name__ == '__main__':
    n = int(input())
    for i in range(n):
        x1, y1, x2, y2, x3, y3 = map(float, input().split())
        points_list = [[x1, y1], [x2, y2], [x3, y3]]
        points_list.sort()
        print(points_list)

        if points_list[0][0] == points_list[1][0]:
            py = (points_list[0][1] + points_list[1][1])/2
            a2_s = (points_list[2][1] - points_list[0][1])/(points_list[2][0] - points_list[0][0])
            a2 = -1/a2_s
            m13x = (points_list[0][0] + points_list[2][0])/2
            m13y = (points_list[0][1] + points_list[2][1])/2
            b2 = m13y - a2*m13x
            px = (py - b2)/a2
        elif points_list[1][0] == points_list[2][0]:
            py = (points_list[1][1] + points_list[2][1])/2
            a2_s = (points_list[2][1] - points_list[0][1])/(points_list[2][0] - points_list[0][0])
            a2 = -1/a2_s
            m13x = (points_list[0][0] + points_list[2][0])/2
            m13y = (points_list[0][1] + points_list[2][1])/2
            b2 = m13y - a2*m13x
            px = (py - b2)/a2
        else:
            a1_s = (points_list[1][1] - points_list[0][1])/(points_list[1][0] - points_list[0][0])
            a1 = -1/a1_s
            a2_s = (points_list[2][1] - points_list[0][1])/(points_list[2][0] - points_list[0][0])
            a2 = -1/a2_s
            m12x = (points_list[0][0] + points_list[1][0]) / 2
            m12y = (points_list[0][1] + points_list[1][1]) / 2
            m13x = (points_list[0][0] + points_list[2][0]) / 2
            m13y = (points_list[0][1] + points_list[2][1]) / 2
            b1 = m12y - a1 * m12x
            b2 = m13y - a2 * m13x
            px = (b2 - b1)/(a1 - a2)
            py = a1*px + b1
        r = math.sqrt(math.pow((px-points_list[0][0]), 2) + math.pow((py-points_list[0][1]), 2))
        print('{0:.3f} {1:.3f} {2:.3f}'.format(px, py, r))

Python: from math import sqrt, fabs


def calcu_cirucumcenter(x1, y1, x2, y2, x3, y3):
    """
   ??????O?????§?¨????(x, y)??¨????????¨
   (x-x1)**2 + (y-y1)**2 = (x-x2)**2 + (y-y2)**2
   x**2 -2*x1*x + x1**2 + y**2 -2*y1*y + y1**2 = ... -2*x2*x, x2**2, -2*y2*y, y2**2
   ?????¨????????¨ (-2*x1 + 2*x2)x + (-2y1 + 2*y2)y + (x1**2 + y1**2 - x2**2 - y2**2) = 0
   x1, x3???????????????????§????
   (-2*x1 + 2*x3)x + (-2y1 + 2*y3)y + (x1**2 + y1**2 - x3**2 - y3**2) = 0
   """
    a = -2 * x1 + 2 * x2
    b = -2 * y1 + 2 * y2
    c = -2 * x1 + 2 * x3
    d = -2 * y1 + 2 * y3
    e = -1* (x1 ** 2 + y1 ** 2 - x2 ** 2 - y2 ** 2)
    f = -1 * (x1 ** 2 + y1 ** 2 - x3 ** 2 - y3 ** 2)

    x = 1 / (a * d - b * c) * (d * e - b * f)
    y = 1 / (a * d - b * c) * (-c * e + a * f)
    return x, y


if __name__ == '__main__':
    epsilon = 1e-9

    # ??????????????\???
    num = int(input())
    for i in range(num):
        x1, y1, x2, y2, x3, y3 = [float(x) for x in input().split(' ')]

        # ?????\????????????(??????)????±???????
        x, y = calcu_cirucumcenter(x1, y1, x2, y2, x3, y3)
        # ?¨????????????¨?????? -0.0 ???????????´???????????¶?????? 0.0 ?????????
        if fabs(x) < epsilon:
            x = 0.0
        if fabs(y) < epsilon:
            y = 0.0

        # ????????????????????§????????¢?????????
        r = sqrt((x - x1)**2 + (x - y1)**2)

        print('{0:.3f} {1:.3f} {2:.3f}'.format(x, y, r))