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JEE Main 20231 FebruaryMorning Shift
Exam
JEE Main
Year
2023
Date
1 February
Shift
Morning Shift
Subject
Mathematics
Chapter
Sets and Relations

JEE Main 2023 · 1 February · Morning Shift · Mathematics · Sets and Relations

Let R be a relation on ℝ , given by R = (a, b): 3a - 3b + 7 is an...

Let RR be a relation on R\mathbb{R}, given by R=(a,b):3a−3b+7 is  an  irrational  number R = { \left(a, b\right): 3a - 3b + \sqrt{7}\text{ is }\text{ an }\text{ irrational }\text{ number } }. Then RR is

Options

  1. AReflexive but neither symmetric nor transitive
  2. BReflexive and transitive but not symmetric
  3. CReflexive and symmetric but not transitive
  4. DAn equivalence relation

Correct answer

A. Reflexive but neither symmetric nor transitive

Step-by-step solution

Given:

R={(a,b):3a−3b+7isirrational}R = \left\{\left(a, b\right): 3a - 3b + \sqrt{7}isirrational\right\}

Reflexive:

3a−3a+7=73a - 3a + \sqrt{7} = \sqrt{7} is irrational.

So, \left(a, a\right) \in R,hence, henceRisreflexive.</p><p>Given:</p><p>is reflexive.</p><p>Given:</p><p>R = \left\{\left(a, b\right): 3a - 3b + \sqrt{7}isirrational\right\}</p><p><strong>Symmetric:</strong></p><p>Let(a,b)∈R</p><p><strong>Symmetric:</strong></p><p>Let \left(a, b\right) \in R, then

3a−3b+73a - 3b + \sqrt{7} is irrational.

So, 3b−3a+73b - 3a + \sqrt{7} is not necessarily irrational, since if 3a=73a = \sqrt{7} and 3b∈Z3b \in Z, then 3a−3b+73a - 3b + \sqrt{7} is irrational., but 3b−3a+73b - 3a + \sqrt{7} is not irrational.

So, \left(a, b\right) \in R ⇒ \left(b, a\right) \in R,hence, henceRisnotsymmetric</p><p><strong>Transitive:</strong></p><p>Take(a,b)is not symmetric</p><p><strong>Transitive:</strong></p><p>Take \left(a, b\right) as \left(\dfrac{\sqrt{7}}{3}, 1\right)and(b,c)and \left(b, c\right) as \left(1, \dfrac{2\sqrt{7}}{3}\right)</p><p>So,(a,b)∈R</p><p>So, \left(a, b\right) \in R and \left(b, c\right) \in Rbut(a,c)∉Rbut \left(a, c\right) \notin R which means relation is not transitive.

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