Set and Closure Property

Learn the definition of set, its mathematical representation, and closure property with examples.

Set

A set is a collection of objects fulfilling the following two properties:

  • Unordered: There’s no particular order of the objects in a set. It doesn’t matter if an object is the first or seventh.
  • Distinct: All objects in the set are distinct.

Set notation

A set is mathematically represented by curly braces { }\{\ \} and is typically denoted by a capital letter. In the case that mentioning all the elements isn’t feasible, we resort to the set builder notation. The set builder notation allows us to represent a set in a concise manner.

Examples of sets

Description Mathematical Representation
Set of natural numbers not exceeding 10 A={1,2,3,4,5,6,7,8,9,10}A = \{1,2,3,4,5,6,7,8,9,10\} \hspace{16mm} A={xA = \{x | xN1x10}x \in N \wedge 1 \le x \le 10\}
Set of 2×22 \times 2 symmetric matrices M={[abbc]M = \bigg\{ \begin{bmatrix} a&b\\b&c \end{bmatrix} | a,b,cR}a,b,c \in \R \bigg\}
Set of linear equations in nn unknowns L={w1x1++wnxn=bL = \{w_1x_1+\cdots + w_nx_n=b
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