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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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