Given: R={(T1,T2):T1. is similar to T2 where T1,T2∈T} and T is the set of all triangles in a plane Reflexive: As we know that, every triangle is similar to itself, so (T1,T1)∈R∀T1∈T Hence, relation R is reflexive. Symmetric: Suppose if (T1,T2)∈R⇒T1 is similar to T2⇒T2 is also similar to T1⇒(T2,T1)∈R. Hence, relation R is symmetric. Transitive: Now suppose, (T1,T2),(T2,T3)∈R⇒T1 is similar to T2 and T2 is similar to T3⇒T1 is similar to T3 . So (T1,T3)∈R. Hence, relation R is transitive. Hence, relation R is an equivalence relation.