title: Error displaying a matplotlib in ipython notebook
body: <p>I'm going though a ipython notebook tutorial and it says to run this in a cell.
      import numpy as np
      import math
      import matplotlib.pyplot as plt</p>
  
  <pre><code>x = np.linspace(0, 2*math.pi) 
  plt.plot(x, np.sin(x), label=r'$\sin(x)$') 
  plt.plot(x, np.cos(x), 'ro', label=r'$\cos(x)$') 
  plt.title(r'Two plots in a graph') 
  plt.legend() 
  </code></pre>
  
  <p>and I should get an actual graph. Isntead I get</p>
  
  <pre><code>&lt;matplotlib.legend.Legend at 0x1124a2fd0&gt;
  </code></pre>
  
  <p>What should I do instead?</p>