Question:

Which of the following is not an empty set?

Updated On: Jul 18, 2023
  • Set of natural numbers $< 1$
  • Natural number between $3$ and $4$
  • The set of integers between $-2$ and $-3$
  • The set $A = \{x: x^2 = 2 \,\forall \,x \,\in\, R\}$
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The Correct Option is D

Solution and Explanation

There is no natural number less than $1$ $\therefore\,$ Option $(a)$ is an empty set. There is no natural number between $3$ and $4$ $\therefore\,$ Option $(b)$ is an empty set. Between two consecutive integers, there exist no integer. So option $(c)$ is an empty set. Now, $x^{2} = 2\,\forall\,x \in R$ $\Rightarrow x = \pm\sqrt{2}$ $\therefore\, A = \left\{-\sqrt{2}, \sqrt{2}\right\}$, which contain elements. $\therefore\,$ It is not an empty set.
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Concepts Used:

Sets

Set is the collection of well defined objects. Sets are represented by capital letters, eg. A={}. Sets are composed of elements which could be numbers, letters, shapes, etc.

Example of set: Set of vowels A={a,e,i,o,u}

Representation of Sets

There are three basic notation or representation of sets are as follows:

Statement Form: The statement representation describes a statement to show what are the elements of a set.

  • For example, Set A is the list of the first five odd numbers.

Roster Form: The form in which elements are listed in set. Elements in the set is seperatrd by comma and enclosed within the curly braces.

  • For example represent the set of vowels in roster form.

A={a,e,i,o,u}

Set Builder Form: 

  1. The set builder representation has a certain rule or a statement that specifically describes the common feature of all the elements of a set.
  2. The set builder form uses a vertical bar in its representation, with a text describing the character of the elements of the set.
  3. For example, A = { k | k is an even number, k ≤ 20}. The statement says, all the elements of set A are even numbers that are less than or equal to 20.
  4. Sometimes a ":" is used in the place of the "|".