# Introduction to Sets

Sets in mathematics are simply collections of distinct objects that form a group. In this step-by-step guide, you will learn more about the definition of sets.

**A step-by-step guide to** **sets**

In mathematics, a set is a well-defined set of objects. Sets are named and displayed in capital letters. In set theory, the elements that make up a set can be anything: people, alphabets, numbers, shapes, variables, etc.

**Elements of a set**

The items in a set are called elements or members of a set. The elements of an array are enclosed in curly braces, separated by commas. To indicate that an element is in a set, the symbol ‘\(∈\)’ is used. If an element is not a member of a set, it is indicated by the symbol ‘\(∉\)’.

**Representation of sets**

Different set symbols are used to represent collections. They differ in how the elements are indexed. The three collection symbols used to represent collections are:

**Semantic form:**

A semantic symbol describes an expression to indicate what the elements of a set are. For example, set \(B\) is a list of five prime numbers.

**Roster form**:

The most common form used to represent sets is roster notation, where the elements of the sets are enclosed in curly brackets separated by commas. For example, Set \(B=\){\(2,4,6,8,10\)}, which is the collection of the first five even numbers. If there is an endless list of elements in a set, then they are defined using a series of dots at the end of the last element.

**Set builder form**:

A set builder symbol has a special rule or expression that specifically describes the common property of all elements of a set. The set builder form uses a vertical bar in its display with text that describes the character of the collection elements.

For example, \(A=\) { \(k | k\) is an odd number, \(k≤ 10\)}. The statement says, all the elements of set \(A\) are odd numbers that are less than or equal to \(10\). Sometimes a “\(:\)” is used in place of the “\(|\)”.

**Types of sets**

A set has many types, such as;

**Empty set or null set:**It has no element present in it.**Finite set:**It has a limited number of elements.**Infinite set:**It has an infinite number of elements.**Equal set:**Two sets that have the same members.**Subsets:**A set ‘\(A\)’ is called to be a subset of \(B\) if each element of \(A\) is also an element of \(B\).**Universal set:**A set that consists of all elements of other sets present in a Venn diagram.

**Sets formulas**

Sets are used in algebra, statistics, and probability. There are some important set formulas are listed below. For both overlapping sets \(A\) and \(B\),

- \(\color{blue}{n\left(A\:U\:B\right)=\:n\left(A\right)\:+\:n\left(B\right)-\:n\left(A\:∩\:B\right)}\)
- \(\color{blue}{n\:\left(A\:∩\:B\right)=n\left(A\right)+n\left(B\right)-n\left(A\:U\:B\right)}\)
- \(\color{blue}{n\left(A\right)=n\left(A\:U\:B\right)+n\left(A\:∩\:B\right)-\:n\left(B\right)}\)
- \(\color{blue}{n\left(B\right)=\:n\left(A\:U\:B\right)+n\left(A\:∩\:B\right)-\:n\left(A\right)}\)
- \(\color{blue}{n\left(A\:-\:B\right)=n\left(A\:U\:B\right)-n\left(B\right)}\)
- \(\color{blue}{n\left(A\:-\:B\right)=\:n\left(A\right)-\:n\left(A\:∩\:B\right)}\)

For any two sets \(A\) and \(B\) that are disjoint,

- \(\color{blue}{n\left(A\:U\:B\right)=n\left(A\right)+\:n\left(B\right)}\)
- \(\color{blue}{A ∩ B = ∅}\)
- \(\color{blue}{n\left(A\:-\:B\right)=n\left(A\right)}\)

**Sets – Example 1:**

** **If set \(A=\) {\(a,b,c\)} and set \(B=\) {\(a,b,c,l,z,r\)}, find \(A ∩ B\).

**Solution:**

\(A∩B=\) {\(a,b,c\)}

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