Title: Trigonometric Delights, Author: Eli Maor
Title: TRIGONOMETRIC FUNCTIONS AND COMPLEX NUMBERS, Author: Desheng Yang
Title: Schaum's Outline of Beginning Calculus, Third Edition, Author: Elliott Mendelson
Title: Pre-Calculus Know-It-ALL, Author: Stan Gibilisco
Title: LEARNING TRIGONOMETRY BY PROBLEM SOLVING, Author: Alexander Rozenblyum
Title: The Doctrine of Triangles: A History of Modern Trigonometry, Author: Glen Van Brummelen