Supplementary books are additional resources that complement primary textbooks or course materials. They provide extra information, examples, and exercises to enhance understanding of a subject. These books can cover various topics, including science, literature, or mathematics, and are often used in educational settings to support learning. These resources can include workbooks, study guides, or reference books. They are particularly useful for students who want to deepen their knowledge or prepare for exams. By using supplementary books, learners can gain different perspectives and improve their skills in a specific area of study.