☼  Finite  &  Infinite  Sets  :   A set in which the process of  counting of  elements surely comes to an end or one can take an upper limit for that set, is called a finite set

A set which is not finite is known as an infinite set. ( can’t take an upper limit )

 e.g. Each one of  the sets given below is a finite set :

  (i) The population on earth.

  (ii) { x : x  N, x < 7 crores }

 e.g. Each one of  the sets given below is an infinite set :

  (i) Set of  all points on the line–segment

  (ii) Set of  all concentric circles with a given centre

  (iii) { x : x  Q, 4 < x < 5 }

  (iv) { x : x  N, x > 100 }

■    Keep in Mind  :   

 The elements of  a set may be listed in any order.

Thus, { 10, 20, 30 }  =  { 10, 30, 20 }  =  { 20, 30, 10 } etc.

 The repetition of  elements in a set is meaningless.

Thus, { 2, 3, 4, 3, 4, 2, 2, 4, 3, 4, 3, 2 }  =  { 2, 3, 4 }.

{ 0 }  { } 0, since    is a set containing no element at all.

{ 0 } and { }are singleton sets and 0 is not a set.

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