text: import math
  import numpy as np
  
  a = 1
  b = math.pi / 2
  
  
  def g(x):
      return math.atan(4 * x)
  
  
  N = 21
  x = np.zeros(N)
  x[0] = (a + b) / 2
  
  for i in range(1, N):
      x[i] = g(x[i - 1])
  
  print(x)
  xs = x[-1]
  print(xs)
  print(math.tan(xs))
  print(4 * xs)
  