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Class 10MathematicsSetsThe Empty Set, Finite and Infinite Sets, Equal SetsMediumLevel 5

How many elements are in the set B = {x : x² = 4, x ∈ N}?

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Answer and explanation

Correct answer: One element

Solving x² = 4 gives x = 2 or x = −2. However, the set specifically restricts x to natural numbers. Under the usual convention that natural numbers are positive counting numbers, 2 is natural but −2 is not. Consequently B = {2}, which has exactly one element and is a singleton set.

Tags

setssingleton-setnatural-numbersquadratic-equationThe Empty SetFinite and Infinite SetsEqual Setsthe empty set finite and infinite sets equal setsMathematicsClass 10 MCQ

Frequently asked questions

What is the correct answer to this question?

One element

Why is this the correct answer?

Solving x² = 4 gives x = 2 or x = −2. However, the set specifically restricts x to natural numbers. Under the usual convention that natural numbers are positive counting numbers, 2 is natural but −2 is not. Consequently B = {2}, which has exactly one element and is a singleton set.

Which subject and chapter does this question cover?

This is a Class 10 Mathematics question. Chapter: Sets. Topic: The Empty Set, Finite and Infinite Sets, Equal Sets.

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