Square

A figure is called simple if it can be divided into a finite number of flat triangles.
For simple shapes, the area is a positive value, the numerical value of which has the following properties:
1. Equal figures have equal areas;
2. If a figure is divided into parts that are simple figures, then the area of ​​this figure is equal to the sum of the areas of its parts.
3. The area of ​​a square with a side equal to the unit of measurement is equal to one.