Chapter 2: Sets

A set is simply a well-defined collection of distinct objects. Sets covers describing them (by listing elements or by a rule), the different types — empty, finite, infinite, equal, subset — and the operations, union, intersection and difference, usually visualised with Venn diagrams. {1,2,3}∩{2,3,4} gives {2,3}; the same two sets united give {1,2,3,4}.

Confusing the subset symbol (⊆) with the element-of symbol (∈) is a frequent slip — one object belongs to a set, while a smaller set is a subset of a larger one. This chapter is largely self-contained, making it a good place to build early confidence in Class 10, and it quietly underlies later work in probability, where an event is itself treated as a set of outcomes.