Define a relation R over a class of n $\times$ n real matrices A and B as
"ARB iff there exists a non-singular matrix P such that PAP$-$1 = B".
Then which of the following is true?
Solution
For reflexive relation,<br/><br/> $\forall(A, A) \in R$ for matrix $P$.<br/><br/>
$\Rightarrow A=P A P^{-1}$ is true for $P=1$<br/><br/>
So, $R$ is reflexive relation.<br/><br/>
For symmetric relation,<br/><br/>
Let $(A, B) \in R$ for matrix $P$.<br/><br/>
$\Rightarrow \quad A=P B P^{-1}$<br/><br/>
After pre-multiply by $P^{-1}$ and post-multiply by $P$, we get<br/><br/>
$P^{-1} A P=B$<br/><br/>
So, $(B, A) \in R$ for matrix $P^{-1}$.<br/><br/>
So, $R$ is a symmetric relation.<br/><br/>
For transitive relation,<br/><br/>
Let $A R B$ and $B R C$<br/><br/>
So, $A=P B P^{-1}$ and $B=P C P^{-1}$<br/><br/>
Now, $A=P\left(P C P^{-1}\right) P^{-1}$<br/><br/>
$\Rightarrow A=(P)^2 C\left(P^{-1}\right)^2 \Rightarrow A=(P)^2 \cdot C \cdot\left(P^2\right)^{-1}$<br/><br/>
$\therefore(A, C) \in R$ for matrix $P^2$.<br/><br/>
$\therefore R$ is transitive relation.<br/><br/>
Hence, $R$ is an equivalence relation.
About this question
Subject: Mathematics · Chapter: Sets, Relations and Functions · Topic: Sets and Operations
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