This book is intended as a textbook for the physics and mathematics faculties of pedagogical institutes in the section "Trigonometry" of a special course in elementary mathematics. it should be considered as a continuation of the book "Special Course of Elementary Algebra," therefore the questions (for example, general provisions of the theory of equations and inequalities) contained in this book and necessary for certain sections of the trigonometry course are not presented in the text, but references are made to the corresponding paragraphs of the "Special Course of Elementary Algebra."