title: Draw more than one function curves in the same plot
body: <p>A way to draw the curve corresponding to a given function is this:</p>
  
  <pre><code>fun1 &lt;- function(x) sin(cos(x)*exp(-x/2))
  plot (fun1, -8, 5)
  </code></pre>
  
  <p>How can I add another function's curve (e.g. fun2, which is also defined by its mathematical formula) in the same plot?</p>