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title: Sets

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# Sets

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## <span style = "color:blue"> In mathematics, a *set* is a collection of things. </span> 

### <span style = "color:red"> The "things" can be  of basically any type we want. </span>

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### <span style="color:blue"> Defining a set is often an important piece of doing mathematics. </span> 

Here are some examples of things:
* "Let A = {1, 2, 3}"
* "Let P be the set of all prime numbers."

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# <span style = "color:red"> Be careful: </span>

1 A **set** can be thought of as a box you put things in. 
2. A **set is not an amount, or a single number**.

### <span style = "color:red"> The following statement is not valid: </span>
"Let $H$ be the set of my height in inches.""

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# Another Example;

* :+1: Let $R$ be the set of people who live in Dr. Penland's house. (I can list the members.)
* :-1: Let $R$ be how many people live in Dr. Penland's house,

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Here are some more examples of things you might see: 

* "We define EVEN to be the set {0,2,4,6,8,...}"
* "We will use RS to denote the set of people who have ever been on the cover of Rolling Stone magazine."

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