text: # coding: utf-8
  import numpy as np
  import matplotlib.pylab as plt
  
  
  def numerical_diff(f, x):
      h = 1e-4 # 0.0001
      return (f(x+h) - f(x-h)) / (2*h)
  
  
  def function_1(x):
      return 0.01*x**2 + 0.1*x 
  
  
  def tangent_line(f, x):
      d = numerical_diff(f, x)
      print(d)
      y = f(x) - d*x
      return lambda t: d*t + y
       
  x = np.arange(0.0, 20.0, 0.1)
  y = function_1(x)
  plt.xlabel("x")
  plt.ylabel("f(x)")
  
  tf = tangent_line(function_1, 5)
  y2 = tf(x)
  
  plt.plot(x, y)
  plt.plot(x, y2)
  plt.show()