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JEE Advanced
Exam
JEE Advanced
Subject
Mathematics
Chapter
Sets and Relations

JEE Advanced · Mathematics · Sets and Relations

A relation on the set of real number R is defined as \ x y: x y>0\...

A relation ρ\rho on the set of real number RR is defined as {xρy:xy>0}.\{x \rho y: x y>0\} . Then, which of the following is/are true?

Options

  1. Aρ\rho is reflexive and symmetric
  2. Bρ\rho is symmetric but not reflexive
  3. Cρ\rho is symmetric and transitive
  4. Dρ\rho is an equivalence relation

Correct answer

C. ρ\rho is symmetric and transitive

Step-by-step solution

We have, xpy:xy>0x p y: x y>0
(i) Reflexive Suppose xρx∈Rx \rho x \in R
⇒
x2>0x^{2} > 0
which is not true when x=0x=0. Hence, relation is not reflexive.
(ii) Symmetric xpy∈R⇒xy>0x p y \in R\Rightarrow \quad x y>0
⇒yx>0\Rightarrow \quad y x>0
⇒yρx∈R\Rightarrow \quad y \rho x \in R
If (x,y)∈R,(x, y) \in \mathbb{R}, then, relation is symmetric.
(iii) Transitive xpy∈R\mathrm{xp} \mathrm{y} \in \mathrm{R}
xy>0x y>0
and yρz∈Ryz>0\quad y \rho z \in Ry z>0
<br/>⇒xy2z>0<br/>⇒xz>0<br/>⇒(x,z)∈R<br/> If (x,y)∈R, then (y,z)∈R<br/>⇒(x,z)∈R<br/>\begin{array}{lc}<br/>\Rightarrow & x y^{2} z>0 \\<br/>\Rightarrow & x z>0 \\<br/>\Rightarrow & (x, z) \in \mathbb{R} \\<br/>\text { If }(x, y) \in \mathbb{R}, \text { then }(y, z) \in \mathbb{R} \\<br/>\Rightarrow & (x, z) \in R<br/>\end{array}
Hence, relation is transitive.$
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