Circular area S=πr?

Circumference C=2πr

Area of a circle: circumference of a circle =πr? :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.

Second, the perimeter formula

1. Perimeter C = 2πr(π:π, r: radius of circle)

2. Rectangular perimeter L=2(a+b)(a and B are the lengths of adjacent sides of the rectangle)

3. Square perimeter L=4a

4. Trapezoidal circumference L=a+b+c+d(a: upper bottom, B: lower bottom, the length of C and D waist, 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.

Three, the circle perimeter area formula

1. Find the area of the known circumference.

S=π[C/(2π)]2

2. Find the perimeter of the known circle area.

C=2π√(π/S)