Mathematic Class XI - NCERT

1.4 Finite and Infinite Sets

Finite Set :- A set which is empty or consists of a definite number of elements is called finite set. 

Infinite Set :- A set which consists of infinite number of elements is called infinite set.

Set	Finite  or Infinite Set
W  =  set of the days of the week	Finite (as number of days in a week are finite, seven)
S = set of solutions of the equation x2 –16 = 0	Finite (as number of solutions are finite, two = degree of the equation.)
G = set of points on a line	Infinite Set ( as the number of points on a line are infinite)

Note :-  infinite set is represented in the roster form by writing a few elements which clearly indicate the structure of the set followed (or preceded) by three dots.

Examples of infinite set :- 

{1, 2, 3 . . .}  is the set of natural numbers

{1, 3, 5, 7, . . .} is the set of odd natural numbers

{. . .,–3, –2, –1, 0,1, 2 ,3, . . .}  is the set of integers.