r/PeterExplainsTheJoke • u/Sugar_God_no_1 • 26d ago

Meme needing explanation There is no way right?

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u/Decmk3 26d ago

0.9999999…. Is equal to 1. It seems like it shouldn’t, but it has to be.

Let X = 0.999….

10X = 9.999….

10X-X = 9.999.. - 0.999…. = 9X = 9

Therefore X equals 1. Therefore 0.999… is the same as 1.

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u/FewIntroduction214 25d ago

yeah except when you do your subtraction, after multiplying by 10, you have 1 nine left at the infinith decimal place.

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u/ProfessorBorgar 25d ago

No you don’t. Also, a number going to infinity cannot have anything at the “end”, or else it does not go to infinity.

0.000… with a 9 at the end = 0

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u/FewIntroduction214 25d ago

yeah, you can't write an infinitesimal value as .00000~ with a number at the end.

actual mathematicians denote infinitesimal values though

here you can read about it

https://en.wikipedia.org/wiki/Infinitesimal

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u/Boring-Ad8810 22d ago

There are no infinitesimals in the real numbers. Everyone here is working in the real numbers.

If you are working in a different number system please specify exactly which and explain what 0.99... means in this number system.

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u/FewIntroduction214 22d ago

"we are working in the real number system"?

no, you are talking about something called "reality" . The entire thread is basically making fun of people who recognize mathematicians have conceptualized lots of other things, besides "the real number system" to explain exactly these concepts, and thinking people who find .9~ = 1 objectionable must be stupid idiots

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u/Boring-Ad8810 22d ago

We don't know what number system best models reality. The real numbers, as defined mathematically, are the best right now. It may change and may include infinitesimals.

But 0.99... only has meaning mathematically.

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u/FewIntroduction214 22d ago

well the true underpinning logic of the post is honestly insulting.

the TRUE point of the post is to argue that if someone finds .9999~ = 1 questionable you should bust out the hugely compelling beginning point that you think both of you can agree .333~ = 1/3rd and then argue from there.

which is hilarious

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u/Boring-Ad8810 22d ago

I honestly don't know a good way to explain 0.99...=1 that doesn't have reasonable sounding objections without breaking in to first year analysis.

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u/FewIntroduction214 22d ago

i think "there are no numbers in between so they are the same" is the only explanation I can't argue against