Open Trigonometry: Basic to Advanced by
Publisher: Wikibooks 2014
Number of pages: 51
Book 1 is pre-calculus trigonometry. We assume the student is relatively new to algebra and do algebra step by step. Many of the pages have closely related free/YouTube videos at the Khan Academy. This is by design. Many students find the video presentation helpful with learning mathematical material.
Mathematics Elementary Algebra & Trigonometry Trigonometry