Pythagorean theorem is a basic theorem in elementary geometry. It has a long history. Almost all ancient civilizations (Greek, China, Egyptian, Babylonian, Indian, etc. ) have studied this theorem. The famous Greek mathematician Pythagoras (580-568- 50 1-500) once studied this theorem, so western countries call this theorem Pythagoras theorem. It is said that Pythagoras likes this theorem very much. When he discovered this theorem around 550 BC, he slaughtered hundreds of cattle and sheep to thank God for his hint. But Pythagoras' proof of Pythagoras theorem has been lost. Euclid (330- 275 BC), a famous Greek mathematician, wrote in his masterpiece "Elements of Geometry" (Volume I, Proposition 47) that he gave a good proof (as shown in figure 1): squares ABFH, AGKC, BCED are made outward from right-angled sides AB, AC and hypotenuse BC of right-angled triangles, and even FC, BK are made into Al ?. Then Euclid proved square ABFH and right-angle BDLM, and square ACCK and right-angle MLEC by means of △BCF and △BCK.
In China, the description of this theorem was first found in the Parallel Computation Classic of the Zhou Dynasty (written in the Western Han Dynasty in the first century BC). In the book (about 1 120), there was a passage asked by the Duke of Zhou, "Hook three, practice four and bend five", which means that the two right sides of a right triangle are 3 and 4 respectively. Take the setting sun as the hook, the height of the sun as the stock, take Pythagoras respectively, and divide it into different ways, and the evil is inclined to the sun. So this sentence clearly states the content of Pythagorean theorem. Zhao Shuang in the Three Kingdoms period (about the 3rd century) once said in his mathematical document Pythagoras Square Diagram (as the annotation of Zhou Kuai Shu Jing) that if the square in the middle was painted yellow, it would be called "middle yellow solid" or "poor solid". He wrote: "According to the string diagram, it can be multiplied by Zhu Shi 2, Zhu Shi 4, Pythagoras difference, medium yellow solid, plus difference solid, which is also called string solid". If we use the present symbols, we can use A, B and C to record the length of hook, strand and chord respectively.