1.

Let R be the relation over the set of all straight lines in a plane such that ℓ1 R ℓ2⬄ ℓ1⊥ ℓ2. Then, R isA. symmetricB. reflexiveC. transitiveD. an equivalence relation

Answer»

A. symmetric

Think of line as a vector quantity:

As ℓ1⊥ ℓ2;

And ℓ2⊥ ℓ1

Hence R is symmetric.

Also Given a relation R over straight lines such that ℓ1⊥ ℓ2

As ℓ1⊥ ℓ2:

⇒ ℓ1. ℓ2=0(DOT PRODUCT)

∵ cos θ =0 as θ =90°;

⇒ This thing is possible if ℓ1 and ℓ2 are symmetric.

E.g. A= 2i-4j and B=-4i-2j

⇒ A. B=-8+8=0



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