title: How to compute derivative in Maxima?
body: <p>I want to calculate the seventh derivative of tan(x) at x=pi/4 in Maxima:</p>
  <pre><code>f(x) := diff(tan(x), x, 7);
  f(%pi / 4);
  </code></pre>
  <p>Yet I cannot get the result. Ay ideas?</p>