1.Relation and Function
easy

$R$ is a relation over the set of real numbers and it is given by $nm \ge 0$. Then $R$ is

A

Symmetric and transitive

B

Reflexive and symmetric

C

A partial order relation

D

An equivalence relation

Solution

Given, $m R n$ iff $m n \geq 0$

Reflexivity:

We know that $m^2 \geq 0$

$\Rightarrow mm \geq 0$

$\Rightarrow mRm$

Hence, $r$ is reflexive.

Symmetry:

Let $m R n$

$\Rightarrow m n \geq 0$

$\Rightarrow nm \geq 0$ (product of real numbers is commutative.)

$\Rightarrow nRm$

Hence, $R$ is symmetric.

Transitive

Let $m R n, n R p$

$\Rightarrow mn \geq 0 ; np \geq 0$

$\Rightarrow m , n , p$ are of same signs

$\Rightarrow mp \geq 0$

$\Rightarrow mRp$

Hence, $R$ is transitive.

Hence, $R$ is an equivalence relation.

Standard 12
Mathematics

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