Circumference c = 2π r

Area of a circle: circumference of a circle = π r? :2πr=(r/2)

The ratio of the area to the circumference of a circle is r/2, that is, it increases with the increase of R radius. The area of a circle is not proportional to its circumference, but is nonlinear proportional.

Extended data

Perimeter formula

1, perimeter c = 2πr(π:π, r: radius of circle)

2. The circumference of the rectangle L = 2 (a+b) (A and B are the lengths of the adjacent sides of the rectangle).

3. Square perimeter L = 4a

4. trapezoid perimeter L = A+B+C+D (A: upper bottom, b: lower bottom, the length of c and d, the same below).

5. The perimeter of the triangle L = A+B+C (A, B and C are the lengths of three sides of the triangle).

6. If the radius is r and the central angle of the sector is n, then the perimeter of the sector is c = 2r+nπ r ÷ 180.

7. The circumference of a semicircle c = π r+2r = π d/2+d.