According to The Orange Grove, "This book covers elementary trigonometry. It is suitable for a one-semester course at the college level, though it could also be used in high schools. The prerequisites are high school algebra and geometry. Contents: 1) Right Triangle Trigonometry. 2) General Triangles. 3) Identities. 4) Radian Measure. 5) Graphing and Inverse Functions. 6) Additional Topics. Appendix A) Answers and Hints to Selected Exercises. Appendix B) Graphing with Gnuplot."
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John Redden (Faculty)
This textbook is very much usable for any beginning Trigonmetry course. http://mecmath.net/trig/index.html I had to supplement the exercise set a bit in a number of sections. Also, I was able to supplement with topics found in the Stitz and Zeager Trigonometry textbook: http://www.stitz-zeager.com/ Also, students found the videos found here to be useful: http://mathispower4u.yolasite.com/trigonometry.php