Plane trigonometry, by S.L. Loney.

Best book for trigonometry but 26$ for this one, wow!! books are really expensive in US. In India I paid 2$ for this

Plane n easy to follow. Good sequential build up on each topic.

This is a book I used in school to study Trigonometry. There are new books now available but i still like this one.

First, I must say that this book covers a large amount of material. Much of the content would be useful for math competitions like the AIME or HMMT. However, the style of writing and the presentation is far too archaic for a modern high school student. Loney's Trigonometry is essentially a collection of 300 or so articles, which possess title such as "To expand sinø in a series of products of factors." This is also a feature of older geometry texts and is off-putting to readers. The book is split into two sections: Triangle Trigonometry and Analytical Trigonometry. Naturally, one would assume that the former discussed solving triangles and related matters, while the latter discussed identities. This is not the case. Triangle trigonometry in the 1800s was apparently today's analytical trigonometry in addition to the "normal" triangle trigonometry. So, what was analytical trigonometry for those scruffy 19th century math teachers? After reading this book, I can safely conclude that it consists of any results in algebra/analysis that involve the sine and cosine functions. The Maclaurin series for the trigonometric functions are discussed, in addition to infinite product expansions; such topics are ordinarily covered in calculus or complex analysis today. The only prerequisite for this book is elementary algebra - the book is therefore a mess of concepts with little logical progression. The final nail in the coffin for this book is that it mentions "irreducible" cubics. The concept of an irreducible cubic is outdated is never used, for irreducible cubics are no different from ordinary cubics.