title: polygon plot is not showing up passing in x and y coordinates
body: <p>I'd like to color the triangular region here under the line that you see so I pass in the vector of x coordinates and y coordinates BUT the region is not shading in.</p>
  
  <p>can you get the region under the line shaded red? the bottom of the region is the x axis and the top is the line. Thank you.</p>
  
  <p>Here is the code:</p>
  
  <pre><code>  x = c(0,1)
     y = c(1,2)
     x
     y
     plot(x,y)
     polygon(x, y, col="red")
  </code></pre>