07/09/2024
Set Theory 🧮🔢
Definitions:
• Set: A collection of distinct, well-defined objects.
• Example: A = {1, 2, 3, 4, 5}
• Element: Each object in a set. For example, 1 is an element of the set A.
• Notation: If 1 belongs to set A, we write 1 ∈ A.
Types of Sets:
1. Finite Set: A set with a limited number of elements.
• Example: {2, 4, 6, 8}
2. Infinite Set: A set with unlimited elements.
• Example: {1, 2, 3, …} (set of natural numbers)
3. Empty Set (∅): A set with no elements.
• Example: {} or ∅
4. Subset: Set A is a subset of set B if all elements of A are in B.
• Notation: A ⊆ B
5. Universal Set: The set that contains all the elements under consideration, usually denoted by U.
• Example: U = {1, 2, 3, 4, 5}
6. Power Set: The set of all subsets of a set.
• Example: If A = {1, 2}, the power set of A is P(A) = {{}, {1}, {2}, {1, 2}}
7. Equal Sets: Two sets are equal if they contain exactly the same elements.
• Example: If A = {1, 2, 3} and B = {1, 2, 3}, then A = B.
8. Disjoint Sets: Two sets that have no elements in common.
• Example: {1, 2} and {3, 4}
Set Operations:
1. Union (A ∪ B): The set containing all elements from A and B.
• Example: If A = {1, 2} and B = {2, 3}, then A ∪ B = {1, 2, 3}
2. Intersection (A ∩ B): The set containing only elements common to both A and B.
• Example: If A = {1, 2} and B = {2, 3}, then A ∩ B = {2}
3. Difference (A − B): The set containing elements of A that are not in B.
• Example: If A = {1, 2, 3} and B = {2, 4}, then A − B = {1, 3}
4. Complement (A’): The set of all elements in the universal set that are not in A.
• Example: If U = {1, 2, 3, 4, 5} and A = {1, 2}, then A’ = {3, 4, 5}
Practical Applications:
• Data Grouping: Sets help in organizing objects or data in groups.
• Probability: Sets are used in events and probability theory.
• Database Systems: In relational databases, sets are used to define relations, queries, and constraints.
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