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Pythagorean Theorem proof in a 2100 year old Chinese book

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Re: Pythagorean Theorem proof in a 2100 year old Chinese book

#41

My understanding is that the 3-4-5 relationship was known for a long, long time before Pythagorus. I think the ancient Egyptians knew of the relationship. But that's not the same thing as a proof: meaning, the fact has been integrated with the fundamentals of a wider body of knowledge. I see the illustration, but I don't understand how that's a "proof."

Also, Pythagoras was ~2500 years ago, before this thing.

Re: Pythagorean Theorem proof in a 2100 year old Chinese book

#42
post #31

Earlier quoted context omitted.

It's familiar from hands-on science museums to see a particular case of the Pythagorean theorem illustrated concretely with diagrams or liquid on a rotating plexiglass panel... But surely those aren't proofs, just illustrations. A proof needs to abstract over all possible right-angle triangles.

Both diagrams are a proof over all right-angle triangles, if you know algebra. See the very first comment after the images.

Hmmm. Maybe I'm just used to the convincing generality of the similarity argument (from Euclid, via Polya): https://math.berkeley.edu/~giventh/papers/eu.pdf

But also, we can't trust geometrical diagrams: https://en.wikipedia.org/wiki/Missing_square_puzzle

Re: Pythagorean Theorem proof in a 2100 year old Chinese book

#43
post #41

My understanding is that the 3-4-5 relationship was known for a long, long time before Pythagorus. I think the ancient Egyptians knew of the relationship. But that's not the same thing as a proof: meaning, the fact has been integrated with the fundamentals of a wider body of knowledge. I see the illustration, but I don't understand how that's a "proof."

Also, Pythagoras was ~2500 years ago, before this thing.

Exactly, by the time this book existed 2100 years ago, the idea should have been traveling all over the place anyway. It's not like ancient civilizations were not connected at all.

Re: Pythagorean Theorem proof in a 2100 year old Chinese book

#44

Earlier quoted context omitted.

Doesn't the PRC's claim on Taiwan boil down to a combination of right-of-conquest ("Taiwan belonged to the Republic of China, we beat up the Republic of China, therefore Taiwan is ours") and Just Because? ("The PRC is the only legitimate Chinese government because the PRC says so") I'm very skeptical of purely historical claims of sovereignty. If the people of Taiwan legitimately vote to join the PRC, that's their ri…

It must be clarified that mainland of China is also part of ROC according to ROC government[1]. In fact, the mainland and taiwan are in war, just like the Union and Confederacy in American civil war, even if there is not military conflicts right now. More interestingly, ROC actually claims larger territory than PRC (for example, part of Mongolia). It is ROC's constitution, not PRC's government, demands taiwan is part…

It would be rather peculiar if during the American Civil War the Confederates had retreated to something like Cuba and remained there to this day.

Re: Pythagorean Theorem proof in a 2100 year old Chinese book

#45

Any ideas of it's authentic? China is hyper nationalist so I'm initially skeptical. Might be as fictitous as their GDP figures or sovereignty over Taiwan.

When you want to like Taiwan more but then notice their view of Tibet is just as twisted District 13

Both sides of that conflict were chock full of assholes.

Re: Pythagorean Theorem proof in a 2100 year old Chinese book

#46
post #37
post #27

Earlier quoted context omitted.

The GP is talking about the straight-faced lie that the PRC peddles in international circles that Taiwan is a province of the mainland government. It is the international equivalent of putting their hands on their ears and shouting "LA LA LA I CAN'T HEAR YOU!", and about as legitimate as Mexico's claim to Texas.

I've ended dates over this with Chinese girls. Inevitably they condescend to me about how "I'm just an American" that "can't understand the complicated situation," but that I should rest assured that "Taiwan is not a country, it is a Chinese province." Never mind the fact that I lived there, documented the sunflower protests, speak the language... As opposed to these girls that hadn't even visited the nation. Because…

Did you say "prove it, take the plane there", and how did they respond to the fact that you need a special visa?

Re: Pythagorean Theorem proof in a 2100 year old Chinese book

#47
I don't know Chinese, but I don't like the explanation in English at the side. I think that both diagrams are part of the same proof, not two independent proofs. I agree with the first comment by Martin Cohen http://disq.us/p/1h6y5qx

> The way I read it is that the first diagram says that(a+b)^2 = 4(ab/2)+c^2 and the second says that c^2 = 4(ab/2)+(a-b)^2. Both of these simplify to c^2 = a^2+b^2.

I only have a small proposed stylistic change that is to keep the are of the triangles as unknown values, let's call it T. So the first diagram shows that (a+b)^2 = 4T + c^2 and the second that c^2 = 4T + (a-b)^2. And simplifying you get simplify to c^2 = a^2 + b^2.

Is there a transcript and translation of the Chinese text?

Re: Pythagorean Theorem proof in a 2100 year old Chinese book

#48

I worry that China is outcompeting us.

Who gives a shit? It is almost always Americans making such statements, obsessed as they are about being number one. If Chine gets richer and more technologically advance that would be good for them and good for us westerners. It is not a zero sum game.

Although to be realistic I don't think China will ever outcompete the US. Not because I don't want them to, but simply because so many fundamentals count in Americas favor and against China. China is facing a demographic catastrophe. The US can easily grow its population with immigration and has plenty of land and natural resources to do so.

Re: Pythagorean Theorem proof in a 2100 year old Chinese book

#49

My understanding is that the 3-4-5 relationship was known for a long, long time before Pythagorus. I think the ancient Egyptians knew of the relationship. But that's not the same thing as a proof: meaning, the fact has been integrated with the fundamentals of a wider body of knowledge. I see the illustration, but I don't understand how that's a "proof."

>I see the illustration, but I don't understand how that's a "proof."

That's an illustration of the proof. Here is a more modern, animated example: https://upload.wikimedia.org/wikipedia/commons/2/29/Pythagor... The Chinese proof looks more like this one though: https://i.stack.imgur.com/Ylzhg.gif There is also explanation in the annotations.

Re: Pythagorean Theorem proof in a 2100 year old Chinese book

#50
From what I understand, the Chinese had often recorded many facts about nature and mathematics very early and accurately. However they never really created much laws. Laws of nature was a western invention. E.g. they observed accurately planetary movements, but never attempted to formulate the laws governing those movements. That sort of thinking was crucial for scientific thinking.
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