1.Relation and Function
hard

Let $P ( S )$ denote the power set of $S =\{1,2,3, \ldots, 10\}$. Define the relations $R_1$ and $R_2$ on $P(S)$ as $A R_1 B$ if $\left( A \cap B ^{ c }\right) \cup\left( B \cap A ^{ c }\right)=\varnothing$ and $AR _2 B$ if $A \cup B ^{ c }=$ $B \cup A ^{ c }, \forall A , B \in P ( S )$. Then :

A

both $R_1$ and $R_2$ are equivalence relations

B

only $R_1$ is an equivalence relation

C

only $R_2$ is an equivalence relation

D

both $R_1$ and $R_2$ are not equivalence relations

(JEE MAIN-2023)

Solution

$S=\{1,2,3, \ldots \ldots .10\}$

$P ( S )=$ power set of $S$

$AR , B \Rightarrow( A \cap \overrightarrow{ B }) \cup(\overrightarrow{ A } \cap B )=\phi$

$R 1$ is reflexive, symmetric

For transitive

$( A \cap \overrightarrow{ B }) \cup(\overrightarrow{ A } \cap B )=\phi ;\{ a \}=\phi=\{ b \} A = B$

$( B \cap \overrightarrow{ C }) \cup(\overrightarrow{ B } \cap C )=\phi \therefore B = C \therefore A = C \text { equivalence. }$

$R _2 \equiv A \cup \overrightarrow{ B }=\overrightarrow{ A } \cup B$

$R _2 \rightarrow \text { Reflexive, symmetric }$

for transitive

$\begin{array}{l} A \cup \overrightarrow{ B }=\overrightarrow{ A } \cup B \Rightarrow\{ a , c , d \}=\{ b , c , d \} \\ \{ a \}=\{ b \} \therefore A = B \\ B \cup \overrightarrow{ C }=\overrightarrow{ B } \cup C \Rightarrow B = C \\ \therefore A = C \quad \therefore A \cup \overrightarrow{ C }=\overrightarrow{ A } \cup C \therefore \text { Equivalence }\end{array}$

Standard 12
Mathematics

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