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Sets and Binary Operations

  • Understand the concept of a set and its basic operations.
  • Learn about binary operations and their properties.
  • Explore examples of binary operations.

Introduction to Sets

A set is a collection of distinct objects, considered as an object in its own right. For example, the set of natural numbers \( \{1, 2, 3, \ldots\} \). Sets can be represented using curly braces, e.g., \( \{a, b, c\} \).

Basic Set Operations

  • Union: The union of sets \(A\) and \(B\) is the set of elements that are in \(A\), \(B\), or both. Denoted as \(A \cup B\).
  • Intersection: The intersection of sets \(A\) and \(B\) is the set of elements that are in both \(A\) and \(B\). Denoted as \(A \cap B\).
  • Difference: The difference of sets \(A\) and \(B\) is the set of elements that are in \(A\) but not in \(B\). Denoted as \(A - B\).
  • Complement: The complement of a set \(A\) is the set of elements not in \(A\).
  • Cartesian Product: The Cartesian product of sets \(A\) and \(B\) is the set of ordered pairs \((a, b)\), where \(a \in A\) and \(b \in B\). Denoted as \(A \times B\).

Binary Operations

A binary operation on a set \(S\) is a rule that combines any two elements of \(S\) to form another element of \(S\).

  • Addition: On the set of integers \( \mathbb{Z} \): \(a + b = c\), where \(a, b, c \in \mathbb{Z}\).
  • Multiplication: On the set of real numbers \( \mathbb{R} \): \(a \cdot b = c\), where \(a, b, c \in \mathbb{R}\).
  • Concatenation: On the set of strings: \(a \circ b = c\), where \(a, b, c\) are strings.

Exercises

  • Set Operations:
    • Given sets \(A = \{1, 2, 3\}\) and \(B = \{3, 4, 5\}\), find \(A \cup B\), \(A \cap B\), and \(A - B\).
    • Determine the Cartesian product \(A \times B\) for sets \(A = \{x, y\}\) and \(B = \{1, 2\}\).
  • Binary Operations:
    • For the set of integers \( \mathbb{Z} \), verify if the addition operation is associative and commutative.
    • For the set of real numbers \( \mathbb{R} \), determine the identity element for the multiplication operation.

Summary

In this lesson, we introduced the concept of sets and their basic operations, such as union, intersection, and Cartesian product. We also explored binary operations and their properties. Understanding these fundamental concepts is essential as we move forward in studying more complex algebraic structures in abstract algebra.

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