Let R be the relation over the set of straight lines of a plane ,such that l1Rl2 ⇔l1 ⊥ l2   Then R is

l1R l1⇒    l1 is not perpendicular to   l1R is not reflexive  l1 R l 2 ⇒ l1⊥l 2⇒ l2⊥l 1⇒ l2 R l 1 ∴ Hence R is symmetric l1Rl2  and l2R l3 ⇒l1Rl3 ∴R is not transitive