Practicing Success

Target Exam

CUET

Subject

-- Mathematics - Section B1

Chapter

Relations and Functions

Question:

For real numbers a and b, define aRb if $b-a +\sqrt{5}$ is an irrational number. Then the relation R is :

Options:

Symmetric

Reflexive

Transitive

Equivalence

Correct Answer:

Reflexive

Explanation:

The correct answer is Option (2) → Reflexive

$aRb=b-a +\sqrt{5}$

R is reflexive → as for all $a∈R$, (a, a) ∈ Relation

as $a-a+\sqrt{5}=\sqrt{5}$ (always irrational)

R not symmetric → let $b=\sqrt{5},a=2$

so (a, b) ∈ Relation as $\sqrt{5}-2+\sqrt{5}$ is irrational

but (b, a) ∉ Relation as $2-\sqrt{5}+\sqrt{5}=2$ is not irrational

R is not transitive →

$(1+\sqrt{5},4)∈R$ as $1+\sqrt{5}-1+\sqrt{5}=-3+2\sqrt{5}$ (irrational)

$(4,2\sqrt{5})∈R$ as $4-2\sqrt{5}+\sqrt{5}=4-\sqrt{5}$ (irrational)

$(1+\sqrt{5},2\sqrt{5})∉R$ as $1+\sqrt{5}-2\sqrt{5}=0$ (not irrational)