Trigonometry is the branch of math that (as the name indicates) focuses on the relationships and sides of triangles. While you might think that the study of a single shape would have a very narrow scope of application. Trigonometry was historically used in astronomy and geography mostly for its navigation and wayward applications. The physics and engineering applications of trig are boundless. Just about every modern structure on the planet was developed and constructed using many of the root principles of trigonometry.
You will find worksheets that include arithmetic of triangles, comparisons, understandings of variation, the use of coordinate grids, Pythagorean properties, trig identities and sequences.