Trigonometric formulae?---No one uses them anymore

Abstract

The title paraphrases a comment made during talks with local mathematics teachers in Townsville. The challenge was laid down. Where are these formulae used? Why do we think they are important? This paper covers some of the answers. In particular, these formulae were used (almost unnoticed) in a project looking at solving the Helmholtz equation on various regions in two dimensions. Some results of this project are presented.