Pythagoras theorem is called Pythagoras theorem in the west, and it is said that Pythagoras, a mathematician and philosopher of Pythagoras, first discovered it in 550 BC. In fact, this mathematical theorem was discovered and applied in ancient China much earlier than Pythagoras. If it can't be verified that Dayu's flood control is a long time ago, then the dialogue between Duke Zhou and Shang can be determined in the Western Zhou Dynasty around 1 100 BC, more than 500 years earlier than Pythagoras. Hooking 3 strands, 4 strings and 5 strings is a special application of Pythagorean theorem (32+42=52). So it should be very appropriate to call it Pythagorean Theorem in the field of mathematics now.

In the later book "Nine Chapters of Arithmetic", Pythagorean Theorem got a more standardized general expression. The book Gou Gu Zhang said: "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: "Numbers come from mutual understanding and circle understanding." There is a principle: when the moment of a right triangle gets a right-angled side' hook' equal to 3 and the other right-angled side' chord' equal to 4, then its hypotenuse' chord' must be 5. This truth was summed up when Dayu was in charge of water conservancy. "

From the above conversation, we can clearly see that people in ancient China discovered and applied the pythagorean theorem, an important principle of mathematics, thousands of years ago. Readers who know a little about plane geometry know that the so-called Pythagorean theorem means that in a right triangle, the sum of the squares of two right-angled sides is equal to the square of the hypotenuse.