[Arithmetic 6] Sets. Elements of a set

I. EXAMPLES

_ Set of students of class 6A

_ Set of letters a, b, c

_ Set of one digit even numbers

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II. WRITING METHOD. NOTATIONS

Sets are usually named with capital letters.

Example: Set of one digit even numbers.

A = $\left\{ {0;2;4;6;8} \right\}$

Set of words cam and chanh.

B = $\left\{ {cam,\;chanh} \right\}$

0; 2; 4; 6; 8  are elements of set A

cam, chanh are elements of set B.

Notations: 2 $\in$ A (2 belongs to A), ổi $\notin$ B (ổi does not belong to B)

►Note:

_ Elements of a set are written in two braces { } which are separated by “;” (if its elements are numbers) or by “,”.

_ Each element is listed once, with arbitrary oder of listing.

To write a set, we usually use two ways:

_ Listing elements of the set.

_ Showing characteristic properties of the set.

Example: Write down the set A of natural numbers greater than 8 and less than 14 by two ways, the fill each square with a suitable notation.

Way 1: A = $\left\{ {9;10;11;12;13} \right\}$

Way 2: A = $\left\{ x\in\mathbb{N} / 8<x<14 \right\}$

12 $\boxed{\in}$ A, 16 $\boxed{\notin}$ A

The set is illustracted by a Venn diagram.