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 cmath

class Point(object):
    def __init__(self, x, y):
        self.point = complex(x, y)
    def __str__(self):
        return "x = {0}, y = {1}".format(self.point.real, self.point.imag)

class Triangle(Point):
    def __init__(self, a, b, c):
        self.a = a
        self.b = b
        self.c = c

        self.edgeA = abs(b.point-c.point)
        self.edgeB = abs(c.point-a.point)
        self.edgeC = abs(a.point-b.point)

        self.angleA = Triangle.angle(self.edgeA, self.edgeB, self.edgeC)
        self.angleB = Triangle.angle(self.edgeB, self.edgeC, self.edgeA)
        self.angleC = Triangle.angle(self.edgeC, self.edgeA, self.edgeB)


    def angle(A, B, C):
        return cmath.acos( (B*B+C*C-A*A)/(2*B*C) )



    def circumscribedCircleRadius(self):
        return abs((self.edgeA/cmath.sin(self.angleA))/2)


    def circumscribedCircleCenter(self):
        A = cmath.sin(2*self.angleA)
        B = cmath.sin(2*self.angleB)
        C = cmath.sin(2*self.angleC)
        X = (self.a.point.real*A + self.b.point.real*B + self.c.point.real*C) / (A+B+C)
        Y = (self.a.point.imag*A + self.b.point.imag*B + self.c.point.imag*C) / (A+B+C)
        return complex(X, Y)

line = list(map(float, input().split()))
p1 = Point(line[0], line[1])
p2 = Point(line[2], line[3])
p3 = Point(line[4], line[5])
T = Triangle(p1, p2, p3)
center = T.circumscribedCircleCenter()
print("{0:.4f} {1:.4f} {2:.4f}".format(center.real, center.imag, T.circumscribedCircleRadius()))

Python: import sys
import 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**2 - x2**2 + y1**2 - y2**2
    a2 = 2 * x3 - 2 * y1
    b2 = 2 * y3 - 2 * y1
    c2 = x1**2 - x3**2 + y1**2 - y3**2
    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: import math
n = int(input())

round = lambda x:(x*1000*2+1)//2/1000

for i in range(n):
    x1,y1,x2,y2,x3,y3 = [ float(s) for s in input().split() ]
    r1 = x1*x1 + y1*y1
    r2 = x2*x2 + y2*y2
    r3 = x3*x3 + y3*y3
    x1_x2 = x1 - x2
    y1_y2 = y1 - y2
    x1_x3 = x1 - x3
    y1_y3 = y1 - y3
    r1_r2 = r1 - r2
    r1_r3 = r1 - r3
    if x1_x2 == 0:
        py = r1_r2 / (2*y1_y2)
        px = (r1_r3 - 2*y1_y3*py) / (2*x1_x3)
    else:
        py = (r1_r2 * x1_x3 - r1_r3 * x1_x2) / (2*(y1_y2 * x1_x3 - y1_y3 * x1_x2))
        px = (r1_r2 - 2*y1_y2*py) / (2*x1_x2)
    r = math.sqrt((x1-px)**2 + (y1-py)**2)
    print('{:.3f}'.format(0+px),'{:.3f}'.format(0+py),'{:.3f}'.format(0+round(r)))

Python: from math import sqrt

def circle(x1, y1, x2, y2, x3, y3):
    if x1 == 0:
        dx = 1
        x1 = x1 + dx
        x2 = x2 + dx
        x3 = x3 + dx
    else:
        dx = 0
    if y2 == 0:
        dy = 1
        y1 = y1 + dy
        y2 = y2 + dy
        y3 = y3 + dy
    else:
        dy = 0
    A = [[x1, y1, 1, 1, 0, 0],[x2, y2, 1, 0, 1, 0],[x3, y3, 1, 0, 0, 1]]
#    print(A)
    for i in range(3):
        A[0] = [x/A[0][0] for x in A[0]]
        A[1] = [A[1][j] - A[1][0] * A[0][j] for j in range(6)]
        A[2] = [A[2][j] - A[2][0] * A[0][j] for j in range(6)]
#        print(A)
        for j in range(3):
            A[j] = A[j][1:] + A[j][:1]
        A = A[1:] + A[:1]
#        print(A)
    for i in range(3):
        A[i] = A[i][:3]
#    print(A)
    V = [-x1**2-y1**2, -x2**2-y2**2, -x3**2-y3**2]
    M = [(A[i][0] * V[0] + A[i][1] * V[1] + A[i][2] * V[2]) for i in range(3)]
    xcenter = -0.5 * M[0] - dx
    ycenter = -0.5 * M[1] - dy
    radius = sqrt((M[0]**2) /4 + (M[1]**2) /4 - M[2])
    return xcenter, ycenter, radius

n = int(input())
for line in range(n):
    x1, y1, x2, y2, x3, y3 = map(float, input().split())
    xc, yc, ra = circle(x1, y1, x2, y2, x3, y3)
    print('%.3f %.3f %.3f' % (xc, yc, ra))

Python: from math import sqrt
n = int(input())

for i in range(n):
    l = input()
    x1,y1,x2,y2,x3,y3=map(float,l.split(' '))
    a_2 = (x1 - x2)**2 + (y1 - y2)**2
    b_2 = (x2 - x3)**2 + (y2 - y3)**2
    c_2 = (x3 - x1)**2 + (y3 - y1)**2
    cos_a_2 = (b_2 + c_2 - a_2)**2/(4* b_2 * c_2)
    sin_a_2 = 1 - cos_a_2
    r = round(sqrt(a_2/sin_a_2)/2,3)
    a = (x1**2 - x3**2 + y1**2 - y3**2)*(x2 - x1)
    b = (x1**2 - x2**2 + y1**2 - y2**2)*(x3 - x1)
    c = (y2 - y1)*(x3 - x1)
    d = (y3 - y1)*(x2 - x1)
    py = round((a-b)/(c-d)/2,3)
    a = (x1**2 - x3**2 + y1**2 - y3**2)*(y2 - y1)
    b = (x1**2 - x2**2 + y1**2 - y2**2)*(y3 - y1)
    c = (x2 - x1)*(y3 - y1)
    d = (x3 - x1)*(y2 - y1)
    px = round((a-b)/(c-d)/2,3)
    print('%s %s %s' %(px, py, r))

Python: import math
 
n = int(input())
for i in range(n):
    x1,y1,x2,y2,x3,y3 = map(float,input().split())
    a1,b1,c1 = 2*(x2-x1),2*(y2-y1), (x1**2 - x2 **2 + y1 ** 2 - y2 ** 2)
    a2,b2,c2 = 2*(x3-x1), 2*(y3-y1), (x1**2 - x3 **2 + y1 ** 2 - y3 ** 2)
 
    p1 = (b1*c2 - b2*c1)/(a1*b2 - a2*b1)
    p2 = (c1*a2 - c2*a1)/(a1*b2 - a2*b1)
    r = math.hypot(x1-p1, y1-p2)
    temp = [p1,p2,r]
    ans = map(lambda x:round(x,3),temp)
    print("%03.3f %03.3f %03.3f"%(temp[0],temp[1],temp[2]))

Python: #!/usr/bin/env python
from math import *
def g(x):
	y = (int((1000 * abs(x)) * 2 + 1) // 2) / 1000
	if x < 0:
		y *= -1
	return y
def func(x):
	x1, y1, x2, y2, x3, y3 = x

	vx1 = x2 - x1
	vy1 = y2 - y1
	vx2 = x3 - x1
	vy2 = y3 - y1
	k = (vx2 ** 2 + vy2 ** 2 - vx1 * vx2 - vy1 * vy2) / (vy1 * vx2 - vx1 * vy2) / 2
	x = vx1 / 2 + k * vy1 + x1
	y = vy1 / 2 - k * vx1 + y1
	r = sqrt((x1 - x) ** 2 + (y1 - y) ** 2)
	print("{0:.3f} {1:.3f} {2:.3f}".format(g(x), g(y), g(r)))
n = int(input())
for _ in range(n):
	func(list(map(float, input().split())))

Python: import math
for _ in range(int(input())):
    x1,y1,x2,y2,x3,y3=map(float,input().split())
    a,b,c=2*(x2-x1),2*(y2-y1),x1**2-x2**2+y1**2-y2**2
    aa,bb,cc=2*(x3-x1),2*(y3-y1),x1**2-x3**2+y1**2-y3**2
    x,y=(b*cc-bb*c)/(a*bb-aa*b),(c*aa-cc*a)/(a*bb-aa*b)
    print('%.3f %.3f %.3f'%(x,y,math.hypot(x1-x,y1-y)))

Python: # -*- coding: utf-8 -*-
from math import sqrt
# import numpy as np


n = int(input())

for i in range(n):
    tmp = input().split(' ')
    
    a, b, c = [(float(tmp[i]), float(tmp[i+1])) for i in range(0, len(tmp), 2)]
    
    #A = np.array(((a[0], a[1], 1),
    #              (b[0], b[1], 1),
    #              (c[0], c[1], 1)))
    A_tmp1 = 1/(a[0]*b[1] + a[1]*c[0] + b[0]*c[1] - b[1]*c[0] - a[1]*b[0] - a[0]*c[1])
    A_tmp2 = [[b[1]-c[1], -(a[1]-c[1]), a[1]-b[1]],
              [-(b[0]-c[0]),  (a[0]-c[0]), -(a[0]-b[0])],
              [b[0]*c[1] - b[1]*c[0], -(a[0]*c[1] - a[1]*c[0]), a[0]*b[1] - a[1]*b[0]]]
    A = [list(map(lambda x: A_tmp1*x, A_tmp2[i])) for i in range(3)]
    
    #B = np.array((((-(a[0]**2 + a[1]**2))),
    #              ((-(b[0]**2 + b[1]**2))),
    #              ((-(c[0]**2 + c[1]**2)))))
    B = [[-(a[0]**2 + a[1]**2)],
         [-(b[0]**2 + b[1]**2)],
         [-(c[0]**2 + c[1]**2)]]
    
    
    tmp = [sum([A[i][j]*B[j][0] for j in range(3)]) for i in range(3)]
    # tmp = np.dot(np.linalg.inv(A), B)
    print(tmp)
    
    x = -tmp[0]/2
    y = -tmp[1]/2
    r = sqrt((tmp[0]**2 + tmp[1]**2 - 4*tmp[2])/4)
    
    print('{:.3} {:.3} {:.3}'.format(x, y, r))