1.5.1

Sets

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Sets of Objects

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Sets

  • Sets are collections of objects.
  • The objects in a set are called its elements.
  • A set is written using curly brackets:
    • {2,3,4} is the set containing 2,3,4
    • {positive even numbers below 5} = {2,4}
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Universal set

  • The symbol ξ is used for the universal set: the set that contains everything.
  • On a Venn diagram, ξ is everything inside the rectangle.
  • The "complement of a set A" is written as A’
    • It is the set of all the things that aren’t in A.
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Empty set

  • The symbol ∅ is used to the empty set: the set that contains no elements.
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Notation

  • If an element e is in a set A, we use the following notation:
    • eAe \in A
  • If an element d is not in A, we use the following notation:
    • dAd \notin A
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Number of elements

  • The number of elements in a set A is written as n(A).
  • In the example shown here, n({2,3,4}) = 3.

Subsets

As we have seen previously, the universal set contains all elements, and can also contain sets. We say that these sets are subsets of the universal set.

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Subsets

  • Subsets are sets contained within other sets.
  • The set A is a subset of set B if all of the elements in A are also elements in B.
  • For example the set A = {2, 3, 4} has the following subsets:
    • {2, 3}, {3, 4}, {2, 4}, {2}, {3}, {4}, {2,3,4}
  • Every set is its own subset.
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Notation

  • If A is a subset of B, we write:
    • A ⊂ B
  • If C is not a subset of B, we write:
    • C ⊄ B

Jump to other topics

1Numbers

2Equations, Formulae & Identities

3Sequences, Functions & Graphs

4Geometry

5Vectors & Transformation Geometry

6Statistics & Probability

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