Let L be the set of all lines in a plane and R be a relation on L defined by l1R l2 if and only if l1⊥l2 then R is
reflexive
symmetric
transitive
an equivalence relation
L1 is not ⊥L1, so R is not reflexiveL1⊥L2⇒L2⊥L1⇒R is symmetric.L1⊥L2 and L2⊥L3⇒L1∥L3⇒R is not transitive.