Pythagorean Theorem is called Pythagorean Theorem in the West, and it is said that Pythagorean mathematician and philosopher Pythagoras first discovered it in 550 BC. In fact, the ancient people of China discovered and applied this mathematical theorem much earlier than Pythagoras. If Dayu's flood control is too old to be accurately verified, then the dialogue between Duke Zhou and Shang can be confirmed. In the Western Zhou Dynasty around 1 100 BC, it was more than 500 years earlier than Pythagoras. Among them, three strands, four strands and five strands are special applications of Pythagorean theorem (32+42=52). Therefore, it should be very appropriate for mathematics to call it Pythagorean Theorem now.

In the later book "Nine Chapters of Arithmetic", Pythagorean Theorem got a more standardized general expression. "Multiply the hook and the stock separately, then add up their products and make a square root, and you can get the string."

At the beginning of China's earliest mathematical work "Parallel Calculation of Classics in Weeks", there was a dialogue in which the Duke of Zhou asked Shang Gao for mathematical knowledge:

Duke Zhou asked, "I heard that you are very proficient in mathematics. Excuse me: there is no ladder to go up in the sky and no ruler to measure on the ground. So how can we get data about heaven and earth? "

Shang Gao replied: "The number comes from the understanding of the other party and the circle. There is a principle: when one right-angled side' hook' obtained from the moment of a right-angled triangle is equal to 3 and the other right-angled side' chord' is equal to 4, then its hypotenuse' chord' must be 5. This truth was summed up when Dayu was managing water. "

From the above conversation, we can clearly see that people in ancient China discovered and applied Pythagorean theorem thousands of years ago, which is an important principle of mathematics. Anyone who knows a little about plane geometry knows that Pythagorean theorem means that in a right triangle, the sum of the squares of two right angles is equal to the square of the hypotenuse.