Plane and Spherical Trigonometry in three parts
by Henry Bedingfield Goodwin
Publisher: Longmans, Green, and Co. 1907
Number of pages: 296
This treatise in the first instance was intended to serve as an introduction to the study of Navigation and Nautical Astronomy for the junior officers under training in H.M. Fleet. The text covers the theoretical portion of Plane Trigonometry, Spherical Trigonometry, and the examples in the use of logarithms and in the solution of plane and spherical triangles.
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by Mara Landers, Brenda Meery - CK-12 Foundation
A comprehensive book on trigonometry. From the table of contents: Trigonometry and Right Angles; Circular Functions; Trigonometric Identities; Inverse Functions and Trigonometric Equations; Triangles and Vectors; Polar Equations and Complex Numbers.
by W. E. Paterson - Clarendon Press
In this book the trigonometrical ratios are introduced as functions of the angle. The trigonometrical properties of the single angle are treated fully in the early chapters, and the examples apply Trigonometry wherever it may be useful.
by David E. Joyce - Clark University
This website is a short introduction to Trigonometry by a professor at Clark University. It is very easy to follow, is full of animations and study problems for the reader to work through. You should already be familiar with algebra and geometry.
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. Many students find the video presentation helpful.