SET001 · Sets, relations & logic · Classes 9–11
Set notation
A set is a well-defined collection of distinct objects, called elements. Sets are named with capital letters, elements are listed in curly brackets, and x ∈ A means x belongs to A.
A = {…}Set notation
📐 Formula
A = {2, 4, 6, 8}; 4 ∈ A, 5 ∉ A; n(A) = number of elements
✏️ Worked example
A = {2, 4, 6, 8}: 6 ∈ A, 7 ∉ A, and n(A) = 4.
🌍 Where it is used
Grouping data: the set of students in a class, the vowels {a, e, i, o, u}.
❓ Quick check
If A = {1, 3, 5}, which is true?
🏋️ Practice
EasyWrite the set of vowels.
Answer: {a, e, i, o, u}
Mediumn({x, y, z}) = ?
Answer: 3
ChallengeIs {1, 2, 2, 3} a set with 4 elements?
Answer: No: repeated elements count once, n = 3