text: """
  Exercise 4
  ===========
  
  Exercise 4 with matplotlib.
  """
  
  import numpy as np
  import matplotlib.pyplot as plt
  
  plt.figure(figsize=(8, 5), dpi=80)
  plt.subplot(111)
  
  X = np.linspace(-np.pi, np.pi, 256)
  S = np.sin(X)
  C = np.cos(X)
  
  plt.plot(X, C, color="blue", linewidth=2.5, linestyle="-")
  plt.plot(X, S, color="red", linewidth=2.5, linestyle="-")
  
  plt.xlim(X.min() * 1.1, X.max() * 1.1)
  plt.ylim(C.min() * 1.1, C.max() * 1.1)
  
  plt.show()
  