Recently, we learned Pythagorean Theorem. Is a basic theorem in elementary geometry, which means "in a right triangle, the sum of the squares of two right-angled sides is equal to the square of the hypotenuse." Although this theorem has only a simple sentence, it has a very long history, especially its thinking method of "combination of form and number" and "unification of form and number", which has inspired and promoted the development of mathematics in China and even the world. Pythagorean theorem is called Pythagorean theorem in the west, and it is said that Pythagorean mathematician Pythagoras first discovered it in 550 BC. In fact, the ancient people in China discovered and applied this mathematical theorem much earlier than Pythagoras. At the beginning of China's earliest mathematical work "Weekly Parallel Calculation", there was a "mathematical dialogue" between Duke Zhou and Shang Gao: Duke Zhou asked, "I heard that you are very proficient in mathematics. I want to ask: if we don't climb the ladder in the sky and have a ruler to measure the whole earth, how can we get data about the world? " Shang Gao replied: "We have summed up some good ways to understand heaven and earth in practice. For example, if one right-angled side (hook) of a right-angled triangle (moment) is equal to 3 and the other right-angled side (chord) is equal to 4, then its hypotenuse (chord) must be 5. This is called Pythagorean Theorem, which was summed up when Dayu was managing water. " If Dayu's flood control is too old to be verified, then the dialogue between the Duke of Zhou and the Shang Dynasty was determined in the Western Zhou Dynasty around 1 100 BC, more than 500 years earlier than Pythagoras. Among them, 3 strands, 4 strands and 5 strands are special applications of Pythagorean theorem. Ancient mathematicians in China not only discovered and applied Pythagorean Theorem very early, but also tried to prove Pythagorean Theorem in theory very early. Zhao Shuang, a mathematician of the State of Wu in the Three Kingdoms period, was the first to prove the Pythagorean theorem. He created "Pythagorean Square Diagram" and proved Pythagorean theorem in detail through the combination of shape and number. In Pythagoras square graph, the square ABDE is obtained by taking the chord as the side length, which consists of four equal right triangles and a small square in the middle. The area of each right triangle is AB/2; The side length of the small square in the middle is b-a, and the area is (b-a)2. Then there is the following formula: a2+b2=c2. In the Pythagorean chapter of Chapter Nine Arithmetic, the Pythagorean theorem is stated as follows: "Multiply Pythagorean shares separately, then add their products and find a root, and you can get a string." Write this passage into a formula, that is: Chord = (Hook 2+Strand2) (1/2) The discovery and proof of Pythagorean theorem by ancient mathematicians in China has a unique contribution and position in the history of world mathematics. In particular, the thinking method of "combination of form and number" and "unity of form and number" embodied in it is of great significance to scientific innovation. As Wu Wenjun, a contemporary mathematician in China, said, "In China's traditional mathematics, the relationship between quantity and spatial form often develops side by side ... Descartes invented analytic geometry in the17th century, which is the reappearance and continuation of China's traditional thoughts and methods after hundreds of years of pause." When we study Pythagorean Theorem today, we should not only learn to use it to calculate, prove and draw, but also learn and understand its history and the thinking method of "combination of form and number" and "unification of form and number" embodied in it, which is of great significance to our future mathematical development and scientific innovation.