Introduction to Set Theory

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Questions and Answers

Which of the following statements accurately describes the difference between roster notation and set-builder notation?

  • Roster notation defines a set by listing a property its elements must satisfy, while set-builder notation lists all elements within curly braces.
  • Roster notation is used for infinite sets, while set-builder notation is used for finite sets.
  • Roster notation is more abstract than set-builder notation and does not require explicit enumeration of elements.
  • Roster notation lists all elements within curly braces, while set-builder notation defines a set by specifying a property its elements must satisfy. (correct)

Given a universal set $U = {1, 2, 3, 4, 5}$ and a set $A = {1, 3, 5}$, what is the complement of $A$, denoted as $A^c$?

  • $A^c = \{1, 3, 5\}$
  • $A^c = \{\}$
  • $A^c = \{2, 4\}$ (correct)
  • $A^c = \{1, 2, 3, 4, 5\}$

If $A = {2, 4, 6, 8}$ and $B = {4, 8, 12}$, what is the result of $A \cap B$?

  • $A \cap B = \{\}$
  • $\cap B = \{2, 6, 12\}$
  • $A \cap B = \{2, 4, 6, 8, 12\}$
  • $A \cap B = \{4, 8\}$ (correct)

According to DeMorgan's Laws, which of the following is equivalent to $(A \cup B)^c$?

<p>$A^c \cap B^c$ (D)</p> Signup and view all the answers

Given set $A = {1, 2, 3}$, which of the following represents the power set of A, denoted as $P(A)$?

<p>$P(A) = {{}, {1}, {2}, {3}, {1, 2}, {1, 3}, {2, 3}, {1, 2, 3}}$ (C)</p> Signup and view all the answers

If set $A$ has 5 elements, how many elements does its power set, $P(A)$, have?

<p>32 (D)</p> Signup and view all the answers

Let $A = {a, b}$ and $B = {1, 2}$. What is the Cartesian product of $A \times B$?

<p>$A \times B = {(a, 1), (a, 2), (b, 1), (b, 2)}$ (A)</p> Signup and view all the answers

Given $A = {1, 2, 3}$, $B = {3, 4, 5}$, and $C = {5, 6, 7}$, what is $(A \cup B) \cap C$?

<p>$(A \cup B) \cap C = {5}$ (B)</p> Signup and view all the answers

According to the identity law, which of the following expressions is equivalent to $A \cup \emptyset$?

<p>$A$ (A)</p> Signup and view all the answers

Which law states that $A \cap (B \cup C) = (A \cap B) \cup (A \cap C)$?

<p>Distributive Law (B)</p> Signup and view all the answers

Which of the following correctly describes a singleton set?

<p>A set containing exactly one element. (C)</p> Signup and view all the answers

If $A \subseteq B$, which of the following statements is always true?

<p>$A \cup B = B$ (C)</p> Signup and view all the answers

What is the symmetric difference between sets $A = {1, 2, 3}$ and $B = {2, 3, 4}$, denoted as $A \Delta B$?

<p>$A \Delta B = {1, 4}$ (D)</p> Signup and view all the answers

Which of the following sets is considered an infinite set?

<p>The set of natural numbers. (B)</p> Signup and view all the answers

What does the Domination Law state regarding the intersection of a set $A$ with the empty set $\emptyset$?

<p>$A \cap \emptyset = \emptyset$ (D)</p> Signup and view all the answers

Given the sets $A = {1, 2}$ and $B = {2, 3}$, find the value of $(A \cup B) \setminus (A \cap B)$.

<p>{1, 3} (D)</p> Signup and view all the answers

Which of the following correctly expresses the absorption law?

<p>$A \cup (A \cap B) = A$ (D)</p> Signup and view all the answers

If $A \subset B$, which statement is always true?

<p>Every element of A is in B, and A ≠ B. (C)</p> Signup and view all the answers

For any set $A$, what is $(A^c)^c$ equal to, according to the Double Complement Law?

<p>$A$ (C)</p> Signup and view all the answers

How does the cardinality of set A relate to the cardinality of its power set P(A)?

<p>The cardinality of P(A) is always greater than the cardinality of A. (A)</p> Signup and view all the answers

Flashcards

Set Theory

A branch of mathematical logic that studies sets, which are collections of objects.

Set

A well-defined collection of distinct objects, considered as an object in its own right.

Elements (Members)

Objects within a set.

Roster Notation

A way of defining a set by listing all elements within curly braces.

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Set-Builder Notation

Defines a set by specifying a property its elements must satisfy.

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Empty Set (Null Set)

The unique set containing no elements.

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Singleton set

A set with exactly one element.

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Finite Set

A set with a finite number of elements.

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Cardinality

The number of elements in a finite set.

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Infinite Set

A set that is not finite, containing an infinite number of elements.

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Universal Set

The set of all possible elements under consideration in a particular context.

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Union (∪)

The set of all elements that are in A, in B, or in both.

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Intersection (∩)

The set of all elements that are in both A and B.

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Difference (\ or -)

The set of all elements that are in A but not in B.

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Complement (Ac)

The set of all elements in the universal set U that are not in A.

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Symmetric Difference (Δ)

The set of all elements that are in either A or B, but not in both.

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Subset (⊆)

If every element of A is also an element of B.

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Power Set (P(A))

The set of all subsets of A, including the empty set and A itself.

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Cartesian Product (A × B)

The set of all ordered pairs (a, b) where a is in A and b is in B.

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Set Identities

Equations involving sets that are always true.

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Study Notes

  • Set theory is a branch of mathematical logic that studies sets, which are collections of objects
  • Although any type of object can be collected into a set, set theory is applied most often to objects that are relevant to mathematics

Basic Concepts

  • A set is a well-defined collection of distinct objects, considered as an object in its own right
  • Sets are typically denoted using uppercase letters
  • The objects within a set are called elements or members
  • Elements are typically denoted using lowercase letters
  • If an element x belongs to a set A, it is denoted as x ∈ A
  • If x does not belong to A, it is denoted as x ∉ A
  • Sets can be defined in several ways including listing all the elements (roster notation) or defining a property that all elements must satisfy (set-builder notation)
  • Roster notation lists all elements within curly braces, e.g., A = {1, 2, 3}
  • Set-builder notation defines a set by specifying a property its elements must satisfy, e.g., B = {x | x is an even number}

Types of Sets

  • The empty set (or null set) is the unique set containing no elements
  • It is denoted by ∅ or {}
  • A singleton set is a set with exactly one element, e.g., A = {a}
  • A finite set is a set with a finite number of elements
  • The number of elements in a finite set A is called its cardinality, denoted by |A|
  • An infinite set is a set that is not finite, containing an infinite number of elements
  • Examples include the set of natural numbers, integers, and real numbers
  • The universal set is the set of all possible elements under consideration in a particular context
  • It is typically denoted by U

Set Operations

  • The union of two sets A and B, denoted by A ∪ B, is the set of all elements that are in A, in B, or in both
  • Formally, A ∪ B = {x | x ∈ A or x ∈ B}
  • The intersection of two sets A and B, denoted by A ∩ B, is the set of all elements that are in both A and B
  • Formally, A ∩ B = {x | x ∈ A and x ∈ B}
  • The difference of two sets A and B, denoted by A \ B or A - B, is the set of all elements that are in A but not in B
  • Formally, A \ B = {x | x ∈ A and x ∉ B}
  • The complement of a set A, denoted by Ac or A′, is the set of all elements in the universal set U that are not in A
  • Formally, Ac = {x | x ∈ U and x ∉ A}
  • The symmetric difference of two sets A and B, denoted by A Δ B, is the set of all elements that are in either A or B, but not in both
  • Formally, A Δ B = (A ∪ B) \ (A ∩ B)

Set Identities

  • These are equations involving sets that are always true, regardless of the specific sets involved.
  • Identity Law: A ∪ ∅ = A and A ∩ U = A
  • Domination Law: A ∪ U = U and A ∩ ∅ = ∅
  • Idempotent Law: A ∪ A = A and A ∩ A = A
  • Complement Law: A ∪ Ac = U and A ∩ Ac = ∅
  • Commutative Law: A ∪ B = B ∪ A and A ∩ B = B ∩ A
  • Associative Law: (A ∪ B) ∪ C = A ∪ (B ∪ C) and (A ∩ B) ∩ C = A ∩ (B ∩ C)
  • Distributive Law: A ∪ (B ∩ C) = (A ∪ B) ∩ (A ∪ C) and A ∩ (B ∪ C) = (A ∩ B) ∪ (A ∩ C)
  • DeMorgan's Laws: (A ∪ B)c = Ac ∩ Bc and (A ∩ B)c = Ac ∪ Bc
  • Absorption Law: A ∪ (A ∩ B) = A and A ∩ (A ∪ B) = A
  • Double Complement Law: (Ac)c = A

Subsets and Power Sets

  • A set A is a subset of a set B, denoted by A ⊆ B, if every element of A is also an element of B
  • Formally, A ⊆ B if for all x, if x ∈ A, then x ∈ B
  • If A ⊆ B and A ≠ B, then A is a proper subset of B, denoted by A ⊂ B
  • The power set of a set A, denoted by P(A), is the set of all subsets of A, including the empty set and A itself
  • If A has n elements, then P(A) has 2n elements

Cartesian Product

  • The Cartesian product of two sets A and B, denoted by A × B, is the set of all ordered pairs (a, b) where a is in A and b is in B
  • Formally, A × B = {(a, b) | a ∈ A and b ∈ B}
  • The Cartesian product is not commutative, i.e., A × B ≠ B × A unless A = B or one of the sets is empty
  • If A has m elements and B has n elements, then A × B has m * n* elements

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