This is the homepage for the free book Trigonometry, by Michael Corral (Schoolcraft College).


Latest version (2020-09-25): Trigonometry.pdf

Code samples from the book:

Current changelog: changelog.txt

Note: The PDF was built using TeXLive 2011 and Ghostscript 9.27 under Linux (Fedora).
LaTeX source code: trigbook-1.2-src.tar.gz

The book is distributed under the terms of the GNU Free Documentation License, Version 1.3.

Buy at

You can buy a printed and bound paperback version of the book with grayscale graphics for $11 plus shipping at here.

Book Description

This is a text on elementary trigonometry, designed for students who have completed courses in high-school algebra and geometry. Though designed for college students, it could also be used in high schools. The traditional topics are covered, but a more geometrical approach is taken than usual. Also, some numerical methods (e.g. the secant method for solving trigonometric equations) are discussed. A brief tutorial on using Gnuplot to graph trigonometric functions is included.

There are 495 exercises in the book, with answers and hints to selected exercises.

Table of Contents

  1. Right Triangle Trigonometry
  2. General Triangles
  3. Identities
  4. Radian Measure
  5. Graphing and Inverse Functions
  6. Additional Topics


Go here to see a computer program (in the Tcl programming language) for solving triangles.

Click here for a PDF file showing how to use trigonometric identities to find a simple closed-form expression for sin 18° (and consequently cos 18°), which I prepared for my trigonometry class. Since expressions for sin 15° and cos 15° can be found by using the difference formulas for sine and cosine (with 15° = 45° - 30°), the expressions for sin 18° and cos 18° can then be used again with the difference formulas to get sin 3° and cos 3°, and hence the trigonometric functions of any integer multiple of 3°. Part of the purpose of doing this was to show how useful the product-to-sum formulas are; they do not seem to get the attention they deserve in most textbooks these days—something I wanted to rectify when I wrote my book (where I give a few examples of how those identities are used in physics and electrical engineering).


(2021-01-05) Cleaned up the web page to make it less hideous and more consistent with the revamped page for Elementary Calculus.

(2015-07-19) After spending quite a bit of time trying to compile the book correctly with TeX Live 2014—and not succeeding—I decided to give up and go back to TeX Live 2011. The reason for recompiling was to make a few modifications and corrections. See the changelog for details.

(2012-06-14) Version 1.2 of Trigonometry is now out. The biggest change is the update of the license to version 1.3 of the GNU Free Documentation License. This was long overdue, and I felt that there were enough changes in the license to warrant a new version number for the book. I also updated the Gnuplot tutorial in Appendix B to reflect the current version (4.6.0) of the software, as well as some stylistic changes. A few typos were corrected and some clarifications made (thanks to Seth Braver at South Puget Sound Community College for bringing those to my attention). See the changelog for details.

(2011-11-04) Added a PDF file showing how to find an exact expression for sin 18°. Also made the Java applet for 2-dimensional rotation available again, but this time in a Zip file that can be downloaded, so that the user has to run it locally. Though this site is now on a new hosting provider I am still worried about bandwidth usage, which is why I'm hesitant to have the live applet hosted on the site again.

(2011-08-13) In addition to being on a new hosting provider, a new update is out. This is primarily a “maintenance release” to clean up some old code so that it compiles under TeX Live 2010, which appears to handle fonts differently than previous versions; in particular the bbding and dingbat font packages seem a bit buggy (the fonts get substituted, resulting in the wrong symbols being displayed). So I removed the book's dependence on those packages and replaced them with the pifont package, which gives a cleaner interface to the necessary symbols. Similar to the Vector Calculus book, some spacing issues also arose, so those were fixed as well. Additionally, some of the EPS graphics were improved to have consistent fonts. Lastly, one typo was corrected. See the changelog for details.

(2011-06-02) Unfortunately I had to remove the applets demonstrating Thales' Theorem and rotations in the xy-coordinate plane. I received a notice from my web hosting provider today that I was exceeding my bandwidth limit, and that my account would be suspended if I did not reduce the bandwidth within seven days. It's possible that the applets are the culprit; I'll find out soon enough.

(2010-12-01) The printed version available at has (finally!) been updated with all the latest corrections. I had been meaning to do this for a while and finally got around to it.

(2010-05-06) The book is now listed on the CLRN Free Digital Textbook Initiative page. This means that the book met the CLRN (California Learning Resource Network) review criteria. Also created a changelog for documenting the updates/corrections to the book.

(2010-04-18) Created a Java applet demonstrating rotations in two dimensions.

(2010-03-28) The book can now be bought as a printed, bound paperback from

(2010-03-12) Version 1.1 released. The only changes in material are the addition of a section (6.4) on polar coordinates, and a short Sage example was added to Section 6.2.

(2009-08-29) Initial version 1.0 is released.