code: #!/usr/bin/env python
  import matplotlib.pyplot as plt
  import numpy as np
  
  x = np.linspace(-2.4, 0.4, 20)
  y = x * x + 2 * x + 1
  plt.plot(x, y, 'c', linewidth=2.0)
  plt.text(-1.5, 1.8, 'y=x^2 + 2*x + 1',
      fontsize=14, style='italic')
  plt.annotate('minima point', xy=(-1, 0),
      xytext=(-1, 0.3), horizontalalignment='center',
      verticalalignment='top', 
      arrowprops=dict(arrowstyle='->', 
          connectionstyle='arc3'))
   
  plt.savefig('annotate.png')
apis: matplotlib.pyplot.plot numpy.linspace matplotlib.pyplot.text matplotlib.pyplot.savefig