# Relations and Functions Class 12 Notes Mathematics Chapter 1

### CHAPTER AT A GLANCE

• Ordered pair – A pair of objects (elements) taken (listed) in a definite (specific) order is known as an ordered pair. In the ordered pair (ai, bi), ai is known as first element and bi is known as second element.
• Equality of ordered pairs – Two ordered pairs (a1, b1) and (a2, b2) are equal iff a1 = a2 and b1 = b2
• Cartesian product – Let A and B be two non-empty sets, then the set of all distinct ordered pair of the form (ai, bi), where a1 ÎA and b1 ÎB is called
cartesian product of A and B and is denoted by A × B. If A and B have m and
n elements respectively, then, number of order pairs in A × B is equal to m × n.
• Relations – Let A and B be two non-empty sets then every subset of A × B
defines a relation from A to B and every relation from A to B is a subset of A × B.
• Domain (D) and Range (R) of a Relation – If R be a relation from set A to B
then the set of first entries of all ordered pairs in R is called domain and set of
all second entries in all order pairs of R is called range of R.
• Inverse Relation – Let A and B be two sets and let R be a relation from set A to
set B then the inverse of R, denoted by R–1, is a relation from set B to set A
and is defined as.
• Number of Relation – Let A and B be two non-empty finite sets having m and
n elements respectively then the number of relations from A to B is (2)m×n
• Universal Relation – A Relation R in a set A is called a universal relation if R = A × A
• Empty Relation: A relation R in a set A is called an empty relation, if no element
of A is related to any element of A.
• Equivalence Relation – Any relation on a set A which is Reflexive, Symmetric and Transitive is called an equivalence Relation.
• Function: A function from a non-empty set A to a non-empty set B is a relation
from set A to set B such that each element of set A is associated with one and
only one element (i.e. unique element) of set B (i.e. each element of set A is
associated with a unique element of set B)
Note that more than one element of A may be associated with any element of
B but in set B, there may be one or more elements to which no element of set A
is associated.
• Domain – The set A is called the domain of ‘f’ (denoted by Df )
• Co-domain – The set B is called the co-domain of ‘f ’ (denoted by Cf)
• Range – The range of ‘f ’ denoted by Rf is the set consisting of all the image of the elements of the domain A.
• One-One function (Injective) – Let f : A ® B then f is called a one-one function
if no two different elements in A have the same image i.e. different elements in
An associated with different elements in B.
• Onto function (Surjective) : A function f : A ® B is said to be onto function,
if every element of B is the image of some element of A under f.
Note : f : A ® B is onto iff Range of f = B.
• One-One Onto function (Bijective) : A function f : A –> B is said to be one-
one and onto if f is both one-one and onto.
• Many-One – A function f : A –> B is said to be many-one if two or more elements
of set A have the same image in B.
• Even and Odd function – A function f(x) is said to be even function iff
f(–x) = f(x) and A function f(x) is said to be odd function iff f (–x) = – f(x).
• Composition functions – Let f : A –> B and g : B –> C be two functions. Then the composition of f and g, denoted by gof : A –> C given by
• Invertible Function and Inverse Function: A function f : X -> Y is defined to be invertible if there exists a function g : Y ® X such that g of = Ix and fog = Iy . The function g is called the inverse of f and is denoted by f–1 . Thus, f is invertible, then f must be one-one and onto and conversely, if f is one-one and onto, then f must be invertible.

Related Articles: