Elements of a Set

 

Recall the set of football players. Each player who joins the club is called a member or an element of the set. A football trainer is not a member or an element of the set of football players. How about the football watchers, are they members of the set?

 

If A = {SMP students of Year VII of your classmate}, then each student from Year VII of SMP at the same classroom as you is a member of set A. Of course every student from year VIII of SMP at your school is not a member of set A. Are the teachers who teach in your class the members of set A?

 

Now consider set H = {names of days starting with letter S}.

Do you know what days are elements of H? What days are not included in H? In Mathematics, to express  element of a set, the symbol “Δ is used and to express not element of a set, the symbol “Ï” is used.

 

Because Sunday is an element of H, we can write:

Sunday Î H

Meanwhile, Wednesday is not an element of H, so we can write:

Wednesday Ï H

 

Now consider set A = {natural numbers less than five}. Here we can write:

1 Î A,                                   5 Ï A,

2 Î A,              and            7 Ï A,

3 Î A                                  9 Ï A,

4 Î A,                                 11 ÏA.