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What does the mathematical expression 9 ∉ T mean?

1 Answer

sente · Room 204

Dec 14, 2015

$9 \notin T$ $9 !in T$ means that $9$ $9$ is not an element of the set $T$ $T$ .

Explanation:

The symbol $\notin$ $!in$ is used with a set $S$ $S$ and a potential element $a$ $a$ of $S$ $S$ to mean

$a \notin S$ $a !in S$

if and only if $a$ $a$ is not an element of $S$ $S$ . Some people like to say that $a$ $a$ "does not belong" to set $T$ $T$ .

(compare to $\in$ $in$ which implies an element is in a set)

Thus $9 \notin T$ $9 !in T$ means that $9$ $9$ is not an element of the set $T$ $T$

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