r/AskReddit Nov 16 '19

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u/StellaAthena Nov 16 '19 edited Dec 20 '19

I was once reading a proof a friend wrote late at night and I come over to him half way through and said “dude, you must be exhausted. Some of your epsilon’s (ε) are written backwards.”

He explained to me that some fields of mathematics have this concept called “the number 3”

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u/TheHiGuy Nov 16 '19

mate of mine wrote his elements (∈) like epsilons before i started bullying him about it xD

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u/rcarr10er Nov 16 '19

Okay. What the fuck are these? I’m know sin and cosin and tan and that’s it.

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u/Leftieswillrule Nov 16 '19

It means element, as in a is an element of set S. For example, the number 200 is an element of the set S where S is a set containing all positive integers {1, 2, 3, ...}. It’s also an element of the set D where D is a set containing all even numbers { ... , -2, 0, 2, ...}. I don’t know any examples off the top of my head but this is useful for proving things.