The syllabus for the BHU UET BAc in Maths is vast. One single book is not enough to cover it. But having a strong command of 10+2 syllabus is very important. Studying the previous years questions will give you a clear picture of the pattern of questions.
The key syllabus for Maths Hons is:
Relations and Functions and their Notations ( RD Sharma)
The toughest part of the paper has to be Complex Numbers
Previous year papers
Binary system
If you are well versed in the above syllabus you are likely to score good marks.