Finite Sets & Infinite Sets

Finite sets are sets that have a finite number of members. If the elements of a finite set are listed one after another, the process will eventually “run out” of elements to list.

Example:
A = {0, 2, 4, 6, 8, …, 100}
C = {x : x is an integer, 1 < x < 10}

An infinite set is a set which is not finite. It is not possible to explicitly list out all the elements of an infinite set.

Example:
T = {x : x is a triangle}
N is the set of natural numbers
A is the set of fractions

The number of elements in a finite set A is denoted by n(A).

Example:
If A is the set of positive integers less than 12 then
A = {1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11} and n(A) = 11

If C is the set of numbers which are also multiples of 3 then
C = {3, 6, 9, …} and C is an infinite set

If D is the set of integers x defined by –3 < x < 6 then
D = {–2, –1, 0, 1, 2, 3, 4, 5} and n(D) = 8

If Q is the set of letters in the word ‘HELLO’ then
Q = {H, E, L, O } , n(Q) = 4 ← ‘L’ is not repeated.

The following video describes sets and gives more examples of finite and infinite sets.

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