This is Maths: Pythagoras’ theorem

1. Concrete model: Pythagorean water demonstration

2. Representational model: 

The square on the left is dissected into two blue triangles, two red triangles, a green square and a yellow square. The square on the right also has two blue triangles and two red triangles, as well as a light blue square whose sides are the hypotenuse of the triangles. “By subtracting equals from equals, it now follows that the square on the hypotenuse is equal to the sum of the squares on the legs [of the triangles]”.

3. Abstract model:

a²+b² = c²