Is the set H={t|t is a triangle having four sides} empty?
Show that the relation R defined in the set A of all triangles as R={(T1,T2):T1is similar to T2}, is equivalence relation. Consider three right angle triangles T1 with sides 3, 4, 5, T2 with sides 5, 12, 13 and T3 with sides 6, 8, 10. Which triangles among T1,T2 and T3 are related?