title: Plot a continuous function in R
body: <p>How would I plot something like <code>y = a*b</code> in R, where <code>y</code> equals some constant and <code>a,b &gt; 0</code>.</p>
  
  <p>So <code>a*b=5</code> for example. Where it plots that line.  </p>
  
  <p>I've only ever seen passing in lists of values for <code>a</code> and <code>b</code> and plotting <code>y</code> from those values, not plotting a continuous curve.</p>
  
  <pre><code>f &lt;- function(a,b) {a*b}
  </code></pre>
  
  <p>How would I do something like the following in R?</p>
  
  <pre><code>f &lt;- function(a,b) {a*b = 5}
  </code></pre>