How to simplify cos(pi)?

Question

I'am new to Maxima and would like to use it for Denavit-Hartenberg matrices (consists of a lot of cos and sin terms). The problem is, that maxima does not simplify the following expression:

ex: x*cos(pi);

I expect, that Maxima simplifies ex to -x. How can this been done? (ratsimp(ex) and trigsimp(ex) have no effects)

Answer 1

In Maxima's dialect, the correct name of the constant is %pi. With it, it should simplify correctly.