Sets
Although there is no strict formal definition of the concept of a set; when we mention a set, a collection consisting of distinct (well-defined) objects should come to mind. Alternatively, a set is a collection of unique elements brought together without any specific order.
Each of the individual objects that make up a set is called an element (or member) of that set.
In a set, each element is written only once. Changing the order or position of the elements within the set does not change the set itself.
Example:
If \(A\) is the set formed by the digits of the number 1199454: \[ A = \{1, 4, 5, 9\} \]
The number of elements in a set \(A\) is denoted by \(s(A)\) [or \(n(A)\)].
\( \bullet \quad \)Curly brackets (braces) are used to enclose and specify the elements of a set.
Example:
\[ A = \{a, \{a\}, b, c, \{a, b\}\} \quad \text{then} \quad s(A) = 5. \]
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