The area formula of a circle is derived from the area formula of a rectangle. Divide the circle into even blocks and get several small sectors. The more people are divided into circles, the closer these small sectors are to the triangle, and the closer the radius of the sectors is to the height of the triangle. When these small divisions are paired, it becomes a rectangle, and it becomes a rectangle with length C/2=rπ and width R.
The area of this rectangle is length times width =rπ times r=πrr.
π (general constant 3. 14) times the square of the radius, that is
The formula for the area of a circle is s = π r 2.