Go: package main

import (
	"fmt"
	"math"
)

func main() {
	var num int
	fmt.Scan(&num)
	for i := 0; i < num; i++ {
		var x1, y1, x2, y2, x3, y3 float64
		fmt.Scanf("%f%f%f%f%f%f", &x1, &y1, &x2, &y2, &x3, &y3)

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

		// 直線1: ax + by - e = 0
		// 直線2: cx + dy - f = 0
		px := (d*e - b*f) / (a*d - b*c)
		py := (c*e - a*f) / (b*c - a*d)
		r := math.Sqrt((px-x1)*(px-x1) + (py-y1)*(py-y1))
		fmt.Printf("%.3f %.3f %.3f\n", px, py, r)
	}
}

Python: # coding: utf-8

import math

n = int(raw_input())

for i in range(n):
	data = map(float, raw_input().split())
	x1 = data[0]
	y1 = data[1]
	x2 = data[2]
	y2 = data[3]
	x3 = data[4]
	y3 = data[5]

	k = 0.5 * ( (x3-x2)*(x3-x1) + (y3-y2)*(y3-y1) ) / ( (x2-x1)*(y3-y1) + (y2-y1)*(x3-x1) )

	x = 0.5 * (x1 + x2) - k * (y2 - y1)
	y = 0.5 * (y1 + y2) + k * (x2 - x1)

	r = math.sqrt( (x-x1)**2 + (y-y1)**2 )

	print("{:.3f} {:.3f} {:.3f}".format(x,y,r))

Python: def perpendicular_bisector(p, q):
    x = (q[0] - p[0])
    y = (q[1] - p[1])
    return (2 * x, 2 * y, p[0]**2-q[0]**2+p[1]**2-q[1]**2)


def gauss_jordan_elimination(Array):
    # N???M??????Array
    N = len(Array)
    if N == 0:
        return (True, Array)
    else:
        M = len(Array[0])

    A = []
    for i in range(len(Array)):
        A.append(Array[i][:])

    pivot = 0
    L = min(N, M)
    while pivot < L:
        pivot_v = A[pivot][pivot]
        pivot_row = pivot
        for i in range(pivot + 1, L):
            v = max(A[i][pivot], -A[i][pivot])
            if pivot_v < v:
                pivot_row = i
                pivot_v = v
        if pivot_row > pivot:
            for i in range(M):
                A[pivot][i], A[pivot_row][i] = A[pivot_row][i], A[pivot][i]
        if pivot_v == 0:
            return ('False', A)
        inv_pivot = 1 / A[pivot][pivot]
        A[pivot][pivot] = 1
        for i in range(pivot + 1, M):
            A[pivot][i] *= inv_pivot
        for i in range(N):
            if i == pivot:
                continue
            t = -1 * A[i][pivot]
            A[i][pivot] = 0
            for j in range(pivot + 1, M):
                A[i][j] += t * A[pivot][j]
        pivot += 1
    return ('True', A)

n = int(input())
for _ in range(n):
    x1, y1, x2, y2, x3, y3 = map(float, input().split())
    a = list(perpendicular_bisector((x1, y1), (x2, y2)))
    b = list(perpendicular_bisector((x1, y1), (x3, y3)))
    c = [a, b]
    state, c = gauss_jordan_elimination(c)
    x = -c[0][2]
    y = -c[1][2]
    r = ((x - x1)**2 + (y - y1)**2)**0.5
    print('{0:.3f} {1:.3f} {2:.3f}'.format(round(x, 3), round(y, 3), round(r, 3)))

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()

        if points_list[0][0] == points_list[1][0]:
            py = (points_list[0][1] + points_list[1][1])/2
            if points_list[2][1] == points_list[0][1]:
                px = (points_list[0][0] + points_list[2][0])/2
            else:
                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
            if points_list[2][1] == points_list[0][1]:
                px = (points_list[0][0]+points_list[2][0])/2
            else:
                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: import math
n=int(input())
for i in range(n):
    x1,y1,x2,y2,x3,y3=[float(i) for i in input().split()]
    t1=x1*(x2+x3-x1)+y1*(y2+y3-y1)
    t2=x2*(x1+x3-x2)+y2*(y1+y3-y2)
    t3=x3*(x1+x2-x3)+y3*(y1+y2-y3)
    px=(t1*x1+t2*x2+t3*x3)/(t1+t2+t3)
    py=(t1*y1+t2*y2+t3*y3)/(t1+t2+t3)
    r=math.hypot(px-x1,py-y1)
    print("%f %f %f"%(round(px,3),round(py,3),round(r,3)))

Python: import math
n=int(input())
for i in range(n):
    x1,y1,x2,y2,x3,y3=[float(i) for i in input().split()]
    A=math.hypot(x2-x3,y2-y3)**2
    B=math.hypot(x1-x3,y1-y3)**2
    C=math.hypot(x1-x2,y1-y2)**2
    t1=A*(B+C-A)
    t2=B*(A+C-B)
    t3=C*(A+B-C)
    px=(t1*x1+t2*x2+t3*x3)/(t1+t2+t3)
    py=(t1*y1+t2*y2+t3*y3)/(t1+t2+t3)
    r=math.hypot(px-x1,py-y1)
    print("%.3f %.3f %.3f"%(round(px,3),round(py,3),round(r,3)))

Python: n = int(input())
datasets = [0]*n
#datasets[k] == [x1k,y1k,x2k,y2k,x3k,y3k]
for i in range(0,n):
  datasets[i] = list(map(float,input().split()))



for data in datasets:
  x1p2=(data[0]+data[2])
  x1m2=(data[0]-data[2])
  x1p3=(data[0]+data[4])
  x1m3=(data[0]-data[4])
  y1p2=(data[1]+data[3])
  y1m2=(data[1]-data[3])
  y1p3=(data[1]+data[5])
  y1m3=(data[1]-data[5])
  x=(x1p2*x1m2*y1m3+y1p2*y1m2*y1m3-x1p3*x1m3*y1m2-y1p3*y1m3*y1m2)/(2*(x1m2*y1m3-x1m3*y1m2))
  y=(y1p2*y1m2*x1m3+x1p2*x1m2*x1m3-y1p3*y1m3*x1m2-x1p3*x1m3*x1m2)/(2*(y1m2*x1m3-y1m3*x1m2))
  r=((x-data[0])**2+(y-data[1])**2)**(1/2)
  print("{0:.3f} {1:.3f} {2:.3f}\n".format(x,y,r))