"1. ‘Skill in Mathematics’ series is prepared for JEE Main and Advanced papers
2. It is a highly recommended textbook to develop a strong grounding in Trigonometry
3. The book covers the entire syllabus into 4 chapters
4. Each chapter includes a wide range of questions that are asked in the examinations

Good foundational grip is required in the Trigonometry, while you are preparing for JEE Mains & Advanced or any other engineering