9: Appendices
- Page ID
- 134868
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- 9.1: Sets and Set Notation
- A set is a collection of things called elements. For example {1,2,3,8} would be a set consisting of the elements 1,2,3, and 8. To indicate that 3 is an element of {1,2,3,8}, it is customary to write 3∈{1,2,3,8}. We can also indicate when an element is not in a set, by writing 9∉{1,2,3,8} which says that 9 is not an element of {1,2,3,8}. Sometimes a rule specifies a set.