Answer:
Step-by-step explanation:
A set is just a collection of objects, but we need some new words and symbols and diagrams to be able to talk sensibly about sets.
In our ordinary language, we try to make sense of the world we live in by classifying collections of things. English has many words for such collections. For example, we speak of ‘a flock of birds’, ‘a herd of cattle’, ‘a swarm of bees’ and ‘a colony of ants’.
We do a similar thing in mathematics, and classify numbers, geometrical figures and other things into collections that we call sets. The objects in these sets are called the elements of the set.
Describing a set
A set can be described by listing all of its elements. For example,
S = { 1, 3, 5, 7, 9 },
which we read as ‘S is the set whose elements are 1, 3, 5, 7 and 9’. The five elements of the set are separated by commas, and the list is enclosed between curly brackets.
A set can also be described by writing a description of its elements between curly brackets. Thus the set S above can also be written as
S = { odd whole numbers less than 10 },
which we read as ‘S is the set of odd whole numbers less than 10’.
A set must be well defined. This means that our description of the elements of a set is clear and unambiguous. For example, { tall people } is not a set, because people tend to disagree about what ‘tall’ means. An example of a well-defined set is
T = { letters in the English alphabet }.
