Pythagorean theorem is a basic elementary geometric theorem. The sum of squares of two right angles of a right triangle is equal to the square of the hypotenuse. If the two right angles of a right triangle are A and B and the hypotenuse is C, then A? +b？ =c？ , (a, b, c) is called Pythagorean array.

There are about 400 ways to prove Pythagorean theorem, and Pythagorean theorem is one of the most proven theorems in mathematics. Pythagorean theorem is one of the important mathematical theorems discovered and proved by human beings in the early days. It is one of the most important tools to solve geometric problems with algebraic ideas, and it is also one of the ties of the combination of numbers and shapes. "Gousan, Gousi and Xian Wu" is one of the most famous examples of Pythagorean theorem.

The ancient Babylonians knew and applied Pythagorean theorem as early as around 3000 BC, and they also knew many Pythagorean sequences. The ancient Egyptians also applied Pythagorean theorem. In China, Shang Gao put forward a special case of Pythagorean theorem of "three strands, four chords and five". In the west, Pythagoras, an ancient Greek in the 6th century BC, first proposed and proved this theorem. He proved by deduction that the square of the hypotenuse of a right triangle is equal to the sum of the squares of two right angles.