Subset of a setThis lesson will explain what a subset of a set. We will start with a definition Set B is a subset of a set A if and only if every object of B is also an object of A. We write B Í A By definition, the empty set( { } or Æ ) is a subset of every set Now, take a look at the following Venn diagrams. Definition of Venn Diagrams: Venn Diagrams are closed circles, named after English logician Robert Venn, used to represent relationships between sets B = { a, b, c} A = { a, b, c, f} U = { a, b, c, f} Since all elements of B belong to A, B is a subset of A Proper subset: Set B is a proper subset of set A, if there exists an element in A that does not belong to B. we write B Ì A Having said that, B is a proper subset of A because f is in A, but not in B. We write B Ì A instead of B Í A Universal set: The set that contains all elements being discussed In our example, U, made with a big rectangle, is the universal set Set A is not a proper subset of U because all elements of U are in subset A Notice that B can still be a subset of A even if the circle used to represent set B was not inside the circle used to represent A. This is illustrated below: As you can see, B is still a subset of A because all its objects or elements (c, and d) are also objects or elements of A. B is again a proper subset because there are elements of A that does not belong to B A and B are also subsets of the universal set U, but especially proper subsets since there are elements in U that does not belong to A and B In general, it is better to represent the figure above as show below to avoid being redundant: The area where elements c, and d are located is the intersection of A and B. More on this on a different lesson! If you have any questions about the subset of a set, I will be more than happy to answer them. 




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