Set Theory - Introduction
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Questions and Answers

What is a characteristic of the empty set?

  • It is the largest set in set theory.
  • It contains a single element.
  • It is a subset of every set. (correct)
  • It has elements in common with every other set.

If sets A and B are disjoint, which statement is true?

  • Both sets have at least one element in common.
  • Neither set is a subset of the other. (correct)
  • One of the sets must be empty.
  • Both sets can be infinite.

Which of the following is the correct representation of the universal set?

  • A single element set.
  • A rectangle enclosing all other sets. (correct)
  • A circle representing all subsets.
  • An empty set denoted as ∅.

How many empty sets exist in the context of set theory?

<p>Only one empty set. (C)</p> Signup and view all the answers

What is the relationship between rational numbers and complex numbers?

<p>Rational numbers are a subset of complex numbers. (D)</p> Signup and view all the answers

In a Venn diagram, if set A is a subset of set B, how are they represented?

<p>A is entirely within B. (B)</p> Signup and view all the answers

Which of the following correctly describes disjoint sets?

<p>They do not share any elements. (D)</p> Signup and view all the answers

What set notation is used for an empty set?

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

What symbol is used to denote membership in a set?

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

Which of the following correctly specifies the set of positive even integers greater than 0?

<p>{x | x is an even integer, x &gt; 0} (A)</p> Signup and view all the answers

Which of the following statements about sets is false?

<p>A set can contain duplicate elements. (C)</p> Signup and view all the answers

Which set is correctly defined as containing odd positive integers less than 10?

<p>Both A and B (D)</p> Signup and view all the answers

If E = {x | x^2 - 3x + 2 = 0}, what are the elements of set E?

<p>{1, 2} (A)</p> Signup and view all the answers

Which notation is used to list members of a set explicitly?

<p>A = {1, 3, 5, ...} (C)</p> Signup and view all the answers

What does the vertical line '|' signify in set notation?

<p>such that (B)</p> Signup and view all the answers

Which of the following describes the sets F and G if F = {2, 1} and G = {1, 2, 2, 1}?

<p>F and G are identical sets with different representations. (D)</p> Signup and view all the answers

What is the definition of two sets being disjoint?

<p>They have no elements in common. (B)</p> Signup and view all the answers

If sets A and B are disjoint, which statement is true regarding the union of A and B?

<p>A ∪ B = A + B (A)</p> Signup and view all the answers

Which property correctly describes the intersection of sets A and B?

<p>A ∩ B is a subset of A and B. (D)</p> Signup and view all the answers

What can be concluded if A is a subset of B?

<p>A ∩ B = A. (C)</p> Signup and view all the answers

For sets A and B, which theorem states that A ⊆ B, A ∩ B = A, and A ∪ B = B are equivalent?

<p>Theorem 1.4 (D)</p> Signup and view all the answers

If U is the disjoint union of M and F, which of the following is true?

<p>All students at the university are in either M or F. (B)</p> Signup and view all the answers

Which of the following statements about sets A and B is correct?

<p>For any element in A ∪ B, it must belong to A or B. (C)</p> Signup and view all the answers

What is the intersection of sets A and C where A = {1, 2, 3, 4} and C = {2, 3, 8, 9}?

<p>{2, 3} (A)</p> Signup and view all the answers

What is the result of applying DeMorgan’s Law to the expression $(A ∪ B)^C$?

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

Which logical equivalence represents the negation of a disjunction?

<p>¬(p ∨ q) = ¬p ∧ ¬q (B)</p> Signup and view all the answers

What defines a finite set?

<p>It is either empty or contains a specific positive integer number of elements. (A)</p> Signup and view all the answers

Which of the following sets is countably infinite?

<p>The set of even positive integers (C)</p> Signup and view all the answers

What is the dual of the equation $(U ∩ A) ∪ (B ∩ A) = A$?

<p>$(∅ ∪ A) ∩ (B ∪ A) = A$ (C)</p> Signup and view all the answers

How is the notation $n(S)$ used in set theory?

<p>It denotes the number of elements in set S. (D)</p> Signup and view all the answers

Which of the following sets is uncountable?

<p>The unit interval $[0, 1]$ (D)</p> Signup and view all the answers

What is the notation used to denote the empty set?

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

What is the conclusion of Lemma 1.6 regarding the union of two finite disjoint sets A and B?

<p>n(A ∪ B) = n(A) + n(B). (A)</p> Signup and view all the answers

When applying the Inclusion-Exclusion Principle to finite sets A and B, what adjustment is made to avoid overcounting?

<p>Subtract n(A ∩ B) from the sum of n(A) and n(B). (C)</p> Signup and view all the answers

According to Corollary 1.7, what is the correct way to find the number of elements in set A that are not in set B?

<p>n(A extbackslash B) = n(A) - n(A ∩ B) (C)</p> Signup and view all the answers

If set A contains 25 elements and overlaps with set B containing 10 elements, what represents n(A extbackslash B)?

<p>25 - 10 = 15 (B)</p> Signup and view all the answers

How can the count of the complement of a finite subset A within a universal set U be determined?

<p>n(A^C) = n(U) - n(A) (C)</p> Signup and view all the answers

What is a significant property of the sets A and B stated in Lemma 1.6?

<p>Sets A and B must be disjoint. (B)</p> Signup and view all the answers

In the context of the Inclusion–Exclusion Principle, which statement is correct?

<p>It reduces the count by the intersection of the sets. (A)</p> Signup and view all the answers

What is the relationship between the sets A, B, and their intersection in the Inclusion–Exclusion Principle?

<p>n(A ∪ B) is equal to n(A) plus n(B) minus n(A ∩ B). (D)</p> Signup and view all the answers

What does the complement of a set A, denoted by AC, represent?

<p>Elements in U that do not belong to A (D)</p> Signup and view all the answers

Which of the following notations is used for the relative complement of a set B with respect to A?

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

How is the symmetric difference of two sets A and B denoted?

<p>A ⊕ B (D)</p> Signup and view all the answers

If A = {1, 2, 3, 4} and B = {3, 4, 5, 6, 7}, what is the result of A extbackslash B?

<p>{1, 2} (A)</p> Signup and view all the answers

In the expression A ⊕ B = (A ∪ B) extbackslash(A ∩ B), what does A ∪ B represent?

<p>All elements in either A or B (A)</p> Signup and view all the answers

What is the result of the symmetric difference A ⊕ C if A = {1, 2, 3, 4} and C = {2, 3, 8, 9}?

<p>{1, 4, 8, 9} (D)</p> Signup and view all the answers

Which mathematical operation is used to represent the fundamental product of sets A1, A2, ..., An?

<p>A1 ∩ A2 ∩ ... ∩ An (B)</p> Signup and view all the answers

Which of the following correctly represents the relative complement of A with respect to the universal set U?

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

Flashcards

Universal Set (U)

A set that includes all other sets being considered in a particular context. It is the largest set.

Empty Set (∅)

A set with no elements.

Subset

A set is a subset of another set if every element of the first set is also an element of the second set.

Disjoint Sets

Two sets are disjoint if they have no elements in common.

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Venn Diagram

A visual representation of sets using enclosed areas in a plane, where the universal set is represented by a rectangle and other sets by circles within the rectangle.

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Venn Diagram: Overlapping Sets

A diagram where the disks representing sets A and B overlap, showing the elements common to both sets in the overlapping region.

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Venn Diagram: Disjoint Sets

A diagram where the disks representing sets A and B do not overlap, indicating that the sets have no elements in common.

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Venn Diagram: Subset

A visual representation of sets, where the disk representing set 'A' is entirely within the disk representing set 'B', indicating that all elements of 'A' are also elements of 'B'.

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What is a set?

A set is a well-defined collection of objects, called elements or members.

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What does '∈' mean?

The symbol '∈' denotes membership in a set, meaning 'is an element of'. For example, 'a ∈ S' means 'a belongs to set S'.

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How are sets specified?

Sets can be specified by listing their elements (e.g., {1, 2, 3}) or by describing the properties of their elements (e.g., {x | x is an even number}).

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When are sets equal?

Two sets are equal if they contain the same elements, regardless of the order or how they are specified. For example, {2, 1} = {1, 2} is true.

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What is a subset?

A subset of a set contains only elements that are also members of the original set. For example, {1, 2} is a subset of {1, 2, 3}.

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What is the empty set?

A set with no elements is called the empty set, represented by {} or ∅.

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What does '∈/' mean?

The symbol '/' means 'is not an element of'. For example, '3 ∈/ B' means '3 does not belong to set B'.

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How are sets combined?

Sets can be combined using operations like union and intersection. The union of two sets contains all the elements from both sets, while the intersection contains only the elements that are present in both sets.

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Disjoint Union

The combination of all elements from sets A and B, where A and B have no elements in common.

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Intersection Subset

Every element in the intersection of A and B is a member of both A and B.

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Set A is a Subset of the Union

Every element in A is also an element of the union of A and B.

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Set Inclusion and Intersection

Set inclusion (A ⊆ B) is equivalent to stating that the intersection of A and B is equal to A.

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Set Inclusion and Union

Set inclusion (A ⊆ B) is equivalent to stating that the union of A and B is equal to B.

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Proper Subset

A set is a proper subset of another set if all the elements of the first set are also elements of the second set, and the two sets are not equal.

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Complement of a set

The set of elements that belong to the universal set U but not to set A. It's like everything in the universe EXCEPT what's in A.

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Difference (A - B)

The set of elements that belong to set A but not to set B. It's like taking set A and removing anything that's also in set B.

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Symmetric Difference (A ⊕ B)

The set of elements that belong to either set A or set B, but not both. Like taking the union and then removing the intersection.

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Fundamental Product

The set of subsets created by taking all possible combinations of elements from n sets.

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Union of sets

The set of elements that belong to set A or set B, but also to both. Like taking the union and then removing the intersection.

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Intersection of sets

The set of elements that belong to both set A and set B. Like the overlap between two sets.

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Universal Set

The set of all possible elements being considered in a given context.

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Set Identity

A statement in set algebra that is always true for any sets. It holds true for different sets and operations on them.

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Intersection of two sets

The set of elements that belong to both set A and set B.

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Dual of a Set Algebra Equation

The replacement of union (∪) with intersection (∩), intersection (∩) with union (∪), the universal set (U) with the empty set (∅) and the empty set (∅) with the universal set (U) in a set algebra equation.

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Principle of Duality

A principle in set algebra stating that if a set algebra equation E is an identity, then its dual, obtained by replacing operators with their duals, is also an identity.

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Finite Set

A set containing a finite number of elements (including zero).

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Infinite Set

A set with an infinite number of elements.

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Countable Set

A set that can be arranged in a sequence, meaning you can assign a unique number to each element in the set.

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Uncountable Set

A set that cannot be arranged in a sequence, meaning you cannot assign a unique number to each element in the set.

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Cardinality of a Set

The number of elements in a set.

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Lemma 1.6: Disjoint Union

If A and B are disjoint finite sets (no common elements), the number of elements in their union (A ∪ B) is the sum of the number of elements in A and the number of elements in B.

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Corollary 1.7: Set Difference

The number of elements in the set A minus the set B (A\B) is equal to the number of elements in A minus the number of elements that are in both A and B (A ∩ B).

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Corollary 1.8: Complement

The number of elements in the complement of a set A (AC) within a finite universal set U is equal to the number of elements in U minus the number of elements in A.

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Inclusion-Exclusion Principle

The number of elements in the union of two sets A and B (A ∪ B) is equal to the sum of the number of elements in A and the number of elements in B, minus the number of elements that are in both A and B (A ∩ B).

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Corollary 1.10: Three Sets Inclusion-Exclusion

The number of elements in the union of three sets A, B, and C (A ∪ B ∪ C) is calculated by adding the number of elements in each set, subtracting the number of elements in each pair-wise intersection, and finally adding back the number of elements in the intersection of all three sets.

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Study Notes

Set Theory - Introduction

  • Set theory is a fundamental concept in mathematics.
  • Sets are well-defined collections of objects.
  • Elements or members of a set are the objects within it.
  • Capital letters (A, B, X, Y) denote sets, while lowercase letters (a, b, x, y) denote elements.
  • "∈" denotes "is an element of," and "∉" denotes "is not an element of."

Specifying Sets

  • Sets can be defined by listing their elements within braces { }.
  • Sets can also be defined by describing the properties that characterize their elements, with a letter (e.g., x) representing a typical member and a vertical line "|" to read as "such that."

Examples

  • A = {1, 3, 5, 7, 9}
  • B = {x | x is an even integer and x > 0}

Subsets

  • If every element of set A is also an element of set B, then A is a subset of B (A ⊆ B), or B contains A (B ⊃ A).
  • Two sets are equal if they have the same elements, and each is a subset of the other.
  • If A is not a subset of B (A ⊈ B), then at least one member of A does not belong to B.

Universal Set

  • All sets under consideration are usually assumed to belong to a fixed large set, known as the universal set (U).

Empty Set (Null Set)

  • A set with no elements is called the empty set (Ø).
  • There is only one empty set.

Theorem 1.2

  • For any set A, the empty set (Ø) is a subset of A (Ø ⊆ A), and A is a subset of the universal set (A ⊆ U).

Disjoint Sets

  • Disjoint sets have no elements in common.
  • Sets are disjoint unless some of the elements are common.

Venn Diagrams

  • Venn diagrams are pictorial representations of sets.
  • The universal set is represented by a rectangle, and other sets by areas within the rectangle.
  • If A ⊆ B, then the disk for set A is entirely within the disk for set B.
  • If A and B are disjoint, then the disks are separated.

Set Operations - Union

  • The union of sets A and B (A ∪ B) contains all elements that belong to A or to B (or both).
  • The resulting set contains all the elements of both the sets.

Set Operations - Intersection

  • The intersection of sets A and B (A ∩ B) contains all elements that belong to both A and B.
  • The intersection contains common elements between the sets.

Set Operations - Disjoint Union

  • The disjoint union of sets A and B (A ∪ B, where A ∩ B = Ø) contains all elements in A or B, but not both.
  • Sets have no common elements; they do not intersect.

Set Operations - Complement

  • The complement of a set A (AC) is comprised of all elements in the universal set (U) that do not belong to A.

Set Operations - Relative Complement

  • The relative complement of a set B with respect to set A (A\B), is the set of elements that belong to A but not to B.

Set Operations - Symmetric Difference

  • The symmetric difference of sets A and B (A ⊕ B) contains elements that belong to either A or B, but not both.
  • The elements are present in either one of the sets, but not in both.

Finite Sets

  • A set is finite if it is empty or contains a specific positive integer number of elements.

Counting Principle

  • The notation n(S) or |S| represents the number of elements in a set S.

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