Ch 1 — Sets

A set is a well-defined collection of objects. Class 11 builds roster and set-builder notation, subsets, power sets, and Venn-diagram operations used later in relations, functions, and probability.

Well-defined collections

A set is a well-defined collection of objects. Class 11 builds roster and set-builder notation, subsets, power sets, and Venn-diagram operations used later in relations, functions, and probability.

∅ ⊆ A for every set A; A ⊆ A always.
De Morgan: (A ∪ B)′ = A′ ∩ B′ and (A ∩ B)′ = A′ ∪ B′.
Finite vs infinite; equal sets have the same elements.

Read this alongside the official NCERT chapter: Sets — https://ncert.nic.in/textbook.php?kemh1=1-16 (full book index: https://ncert.nic.in/textbook.php?kemh1=0-16).