title: Critical t values in R
body: <p>I need to determine the critical t values for one-sided tails of 75% and 99%, for 40 degrees of freedom.</p>
  
  <p>The following is code for a two-sided 99% critical t values:</p>
  
  <pre><code>qt(0.01, 40)
  </code></pre>
  
  <p>but how can I determine for a one-sided critical t value?</p>