This book is written not only for students who understand mathematics but also for those who do not but are planning to continue their education at university, take mathematical courses and want to avoid a lot of pain and frustration. This book will also be useful for enthusiastic secondary school teachers, who know that study of mathematics is not a memorization of a set of rules and “recipes” that most students will forget soon after the final exam. Teaching mathematics should be based on the development of mathematical thinking, based on creativity, logic, the ability to prove statements, establishing logical connections and solving non-standard problems. The study of mathematics should stimulate the development of mental abilities and intellectual growth. Many students have difficulty mastering the mathematical disciplines taught at school, not because they “lack” the ability, but because they are not taught to understand them.