The concept of relation is used in relating two objects or quantities with each other. Suppose two sets are considered, the relationship between them will be established if there is a connection between the elements of two or more non-empty sets.
Mathematically, “a relation R from a set A to a set B is a subset of the cartesian product A × B obtained by describing a relationship between the first element x and the second element y of the ordered pairs in A × B”.
A function is a relationship which explains that there should be only one output for each input. It is a special kind of relation (a set of ordered pairs) which obeys a rule, i.e. every y-value should be connected to only one y-value.
Mathematically, “a relation f from a set A to a set B is said to be a function if every element of set A has one and only one image in set B”.
NCERT textbook deals with relations and functions, types of relation, types of functions, the composition of functions and invertible function, binary operations and various examples.