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JEE Main 20203 SeptemberEvening Shift
Exam
JEE Main
Year
2020
Date
3 September
Shift
Evening Shift
Subject
Mathematics
Chapter
Sets and Relations

JEE Main 2020 · 3 September · Evening Shift · Mathematics · Sets and Relations

Let R _ 1 and R _ 2 be two relations defined as follows : R _ 1 = \...

Let R1{R}_{1} and R2{R}_{2} be two relations defined as follows :

R1={(a,b)∈R2:a2+b2∈Q}{R}_{1} = \left\{\left(a, b\right) \in {R}^{2}: {a}^{2} + {b}^{2} \in Q\right\} and R2={(a,b)∈R2:a2+b2∉Q}{R}_{2} = \left\{\left(a, b\right) \in {R}^{2}: {a}^{2} + {b}^{2} \notin Q\right\}, where QQ is the set of all rational numbers, then

Options

  1. AR1{R}_{1} is transitive but R2{R}_{2} is not transitive.
  2. BR2{R}_{2} is transitive but R1{R}_{1} is not transitive.
  3. CNeither R1{R}_{1} nor R2{R}_{2} is transitive.
  4. DR1{R}_{1} and R2{R}_{2} are both transitive.

Correct answer

C. Neither R1{R}_{1} nor R2{R}_{2} is transitive.

Step-by-step solution

For& R1{R}_{1}~let& a=1+2,b=1−2,c=814a = 1 + \sqrt{2}, b = 1 - \sqrt{2}, c = 8\dfrac{1}{4}

aR1b⇒a2+b2=(1+2)2+(1−2)2=6∈Qa{R}_{1}b ⇒ a^{2} + b^{2} = \left(1 + \sqrt{2}\right)2 + \left(1 - \sqrt{2}\right)2 = 6 \in Q

bR1c⇒b2+c2=(1−2)2+(814)2=3∈Qb{R}_{1}c ⇒ b^{2} + c^{2} = \left(1 - \sqrt{2}\right)2 + \left(8\dfrac{1}{4}\right)2 = 3 \in Q

aR1c⇒a2+c2=(1+2)2+(814)2=3+42∉Qa{R}_{1}c ⇒ a^{2} + c^{2} = \left(1 + \sqrt{2}\right)2 + \left(8\dfrac{1}{4}\right)2 = 3 + 4\sqrt{2} \notin Q

∴R1∴{R}_{1}~is not transitive.

For& R2{R}_{2}~let& a=1+2,b=2,c=1−2a = 1 + \sqrt{2}, b = \sqrt{2}, c = 1 - \sqrt{2}

aR2b⇒a2+b2=(1+2)2+(2)2=5+22∉Qa{R}_{2}b ⇒ a^{2} + b^{2} = \left(1 + \sqrt{2}\right)2 + \left(\sqrt{2}\right)2 = 5 + 2\sqrt{2} \notin Q

bR2c⇒b2+c2=(2)2+(1−2)2=5−22∉Qb{R}_{2}c ⇒ b^{2} + c^{2} = \left(\sqrt{2}\right)2 + \left(1 - \sqrt{2}\right)2 = 5 - 2\sqrt{2} \notin Q

aR2c⇒a2+c2=(1+2)2+(1−2)2=6∈Qa{R}_{2}c ⇒ a^{2} + c^{2} = \left(1 + \sqrt{2}\right)2 + \left(1 - \sqrt{2}\right)2 = 6 \in Q

∴R2∴{R}_{2}& is not transitive.

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