Math111 Help: Difference between ( ),[ ], and { }

I am confused. My Instructor for the class is not very good help either. I am working on some problems in WebWork and I do not know the difference between those brackets, but WebWork wont accept my answer. Can anyone give me a simple definition of when I would use each of these brackets? Also, when would I use "infinity?"

Some examples are: [8,9), [3, INF), {4,5}, and so on.

Thanks!

[ ] means the point is included in the segment; ( ) means not included.

For example,

[8,9) denotes 8 ≤ x < 9 ;

[3, INF) denotes 3 ≤ x < ∞ ;


{ } typically defines set.

{4, 5} denotes that there are two elements in this set, 4 and 5.

Does it make sense to you now? ;-)