It can be calculated as follows: complete two circles, draw a square with a side length of R in half of the small circle, and then draw a square with a side length of R. The shadow area of the side of the small circle is calculated as a quarter of the small circle plus a quarter of the small circle, MINUS the square with a side length of R, and the number is divided by 4. Half of the circle is the same.

Calculation: 3. 14x20? x 1/4x2-20？ =228

228x 1/4=57

3. 14x30？ x 1/4x2-30？ =5 13

5 13÷4= 128.25

57+ 128.25= 185.25

circumference ratio

The ratio of the circumference to the diameter of a circle is called pi. It is an infinite acyclic decimal, usually represented by the letter π (pronounced "pie").

π ≈ 3. 14159265323846 2643 ... The approximate value is usually 3.14. We can say that the circumference of a circle is π times the diameter, or about 3. 14 times the diameter, but we can't directly say that the circumference of a circle is 3. 14 times the diameter.