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The relation “is parallel to” on a set S of all straight lines in a plane is :(a) Symmetric only (b) Reflexive and Transitive only (c) Transitive only (d) An equivalence relation |
Answer» (d) An equivalence relation Let R = {(x, y) : line x is parallel to line y, x y ∈ set of coplanar straight lines}. • Every line is parallel to itself. So, if x ∈S, then (x, x) ∈R ⇒ R is reflexive • If (x, y) ∈R ⇒ x | | y ⇒ y | | x ⇒ (y, x) ∈R ⇒ R is symmetric • (x, y) ∈R and (y, z) ∈R ⇒ x | | y and y | | z ⇒ x | | z ⇒ (x, z) ∈R ⇒ R is transitive ∴ R being reflexive, symmetric and transitive, it is an equivalence relation. |
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