Zhao Shuang, a mathematician of the State of Wu in the Three Kingdoms period, was the first person in China to prove Pythagorean theorem.

Zhao Shuang created Pythagorean Square Diagram, and gave a detailed proof of Pythagorean Theorem by combining shape numbers.

In the Pythagorean square diagram, the square ABDE with the chord as the side length consists of four congruent right-angled triangles and a small square in the middle.

The area of each right triangle is AB/2; If the side length of the small square in the middle is b-a, the area is (b-a) 2.

Then you can get the following formula:

4×(ab/2)+(b-a)^2=c^2，

After simplification, you can get:

a^2+b^2=c^2