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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

#31
post #29
post #22

Earlier quoted context omitted.

It could've been used without being proved also

The diagrams on the pages shown basically serve as a proof.

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.

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

#33

Wouldn't something from that period be written with seal script? That script looks like modern Han characters with an archaic font - it's completely readable.

Keep in mind that the earliest copies of Euclid, Plato, etc, are often from several hundred or 1000 years later.

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

#34
I know you can use the second diagram to prove the theorem, but it requires an algebraic argument (the other two squares aren't shown). Unless the text says something pretty interesting, this looks more like a proof just for a 3,4,5 triangle.

The first diagram I can't get my head round at all, or is it proving something different?

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

#35
post #31
post #29

Earlier quoted context omitted.

The diagrams on the pages shown basically serve as a proof.

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.

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

#36
post #6

Earlier quoted context omitted.

> sovereignty over Taiwan This is the claim that China and Taiwan should reunite since the PRC drove the Nationalist Party out of mainland China. It isn't fictitious, it's merely a political wish to merge the two from the PRC side. Similarly, some Nationalists in Taiwan are happy to take back mainland China, as much as the country is divided on whether Taiwan should remain as it is, or should declare its full indepen…

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 of China. Though it's not the People's Republic of China. And guess what, according to ROC's constitution, mainland China is "enemy occupied area". Therefore people in mainland China does not have right to vote, or legitimately declare independence.

[1] https://commons.wikimedia.org/wiki/File:ROC_Administrative_a...

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

#37
post #27
post #6

Earlier quoted context omitted.

> sovereignty over Taiwan This is the claim that China and Taiwan should reunite since the PRC drove the Nationalist Party out of mainland China. It isn't fictitious, it's merely a political wish to merge the two from the PRC side. Similarly, some Nationalists in Taiwan are happy to take back mainland China, as much as the country is divided on whether Taiwan should remain as it is, or should declare its full indepen…

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 they can't. Because you need a special visa. To enter this "non-country."

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

#38
post #34

I know you can use the second diagram to prove the theorem, but it requires an algebraic argument (the other two squares aren't shown). Unless the text says something pretty interesting, this looks more like a proof just for a 3,4,5 triangle. The first diagram I can't get my head round at all, or is it proving something different?

The top comment after the images of the two diagrams explains how the 1st diagram is another algebraic proof, similar to the 2nd diagram.

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

#39
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."

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

#40
post #34

I know you can use the second diagram to prove the theorem, but it requires an algebraic argument (the other two squares aren't shown). Unless the text says something pretty interesting, this looks more like a proof just for a 3,4,5 triangle. The first diagram I can't get my head round at all, or is it proving something different?

The first and second diagrams are similar, just using the 'outside' vs 'inside' deconstruction.

If we label the sides a=3, b=4, and c=5 :

The first diagram shows that the big outer square of length (a+b) equals the area of the 4 triangles plus the rotated square of side c. (a+b)^2 = 2ab + c^2

[I'm not sure why they drew an inner 3x3 square on its own].

The second diagram puts the same four triangles inside the rotated square of side c, which leaves an extra smaller square of side (b-a) inside.

c^2 = 2ab + (b-a)^2

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