## The Mathematical Symbol "Not an Element Of (∉)"

The "Not an Element Of" Symbol (∉)

The ∉ symbol is a fundamental notation in set theory used to indicate that a particular element does not belong to a given set. It expresses the non-membership of an element in a set, which is the opposite of the "element of" symbol (∈).

## Understanding ∉

Within the realm of mathematics, particularly in set theory, the concept of belonging or not belonging to a set is crucial. The ∉ symbol represents the latter scenario, where an item is explicitly not a member of a specified set.

Example 1: Basic Use

Consider a set $$A = \{1, 2, 3\}$$ and an element $$x = 4$$. We can say: $x ∉ A$ This statement confirms that the number 4 is not a member of set A.

Example 2: Common Elements

For two sets $$B = \{a, b, c\}$$ and $$C = \{d, e, f\}$$: $a ∉ C$ This indicates that the element 'a' from set B is not present in set C.

## Common Usage of ∉

The ∉ symbol frequently appears in:

• Mathematics: Especially in set theory, the ∉ symbol is used to discuss the elements and their relationships to sets.
• Programming: Programmers may use this concept when checking if an item is absent from a list or an array in certain languages or frameworks.

In summary, the ∉ symbol provides a concise method for discussing the non-inclusion of items in specific sets. Its recognition and understanding are vital for those delving deep into mathematics or programming. ## Are You Good at Mathematical Symbols?

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## Codes for the ∉ Symbol

 The Symbol ∉ Alt Code Alt 8713 HTML Code ∉ HTML Entity ∉ CSS Code \2209 Hex Code ∉ Unicode U+2209

## How To Insert the ∉ Symbol

(Method 1) Copy and paste the symbol.

The easiest way to get the ∉ symbol is to copy and paste it into your document.

Bear in mind that this is a UTF-8 encoded character. It must be encoded as UTF-8 at all stages (copying, replacing, editing, pasting), otherwise it will render as random characters or the dreaded �.

(Method 2) Use the "Alt Code."

If you have a keyboard with a numeric pad, you can use this method. Simply hold down the Alt key and type 8713. When you lift the Alt key, the symbol appears. ("Num Lock" must be on.)

(Method 3) Use the HTML Decimal Code (for webpages).

HTML TextOutput
<b>My symbol: &#8713;</b>My symbol: ∉

(Method 4) Use the HTML Entity Code (for webpages).

HTML TextOutput
<b>My symbol: &notin;</b>My symbol: ∉

(Method 5) Use the CSS Code (for webpages).

CSS and HTML TextOutput
<style>
span:after {
content: "\2209";}
</style>
<span>My symbol:</span>
My symbol: ∉

(Method 6) Use the HTML Hex Code (for webpages and HTML canvas).

HTML TextOutput
<b>My symbol: &#x2209;</b>My symbol: ∉
On the assumption that you already have your canvas and the context set up, use the Hex code in the format 0x2209 to place the ∉ symbol on your canvas. For example:
JavaScript Text
const x = "0x"+"E9"
ctx.fillText(String.fromCodePoint(x), 5, 5);
Output

(Method 7) Use the Unicode (for various, e.g. Microsoft Office, JavaScript, Perl).

The Unicode for ∉ is U+2209. The important part is the hexadecimal number after the U+, which is used in various formats. For example, in Microsoft Office applications (e.g. Word, PowerPoint), do the following:
TypeOutput
2209
[Hold down Alt]
[Press x]

(The 2209 turns into ∉. Note that you can omit any leading zeros.)
In JavaScript, the syntax is \uXXXX. So, our example would be \u2209. (Note that the format is 4 hexadecimal characters.)
JavaScript TextOutput
let str = "\u2209"
document.write("My symbol: " + str)
My symbol: ∉