code: def ex6_2(n):
      
      x = np.zeros(len(n))
      for k, nn in enumerate(n):
          if nn >= -2 and nn <= 5:
              x[k] = 8 - nn
      return x
docs: Generate a triangle pulse as described in Example 6-2
      of Chapter 6.
      
      You need to supply an index array n that covers at least [-2, 5]. 
      The function returns the hard-coded signal of the example.
      
      Parameters
      ----------
      n : time index ndarray covering at least -2 to +5.
      
      Returns
      -------
      x : ndarray of signal samples in x
      
      Examples
      --------
      >>> import numpy as np
      >>> import matplotlib.pyplot as plt
      >>> from sk_dsp_comm import sigsys as ss
      >>> n = np.arange(-5,8)
      >>> x = ss.ex6_2(n)
      >>> plt.stem(n,x) # creates a stem plot of x vs n