NCERT Example 1 - Relations and Functions
Question: Let A be the set of all students of a boys school. Show that R = {(a, b) : a is sister of b} is the empty relation and R' = {(a, b) : the difference between heights of a and b is less than 3 metres} is the universal relation.
Answer: R = empty set (empty relation); R' = A x A (universal relation).
Full step-by-step NCERT solution with diagrams on Something by Zero.