Circumference:

The circumference of a rectangle = (length+width) × 2 = 2 (a+b) = (a+b) × 2.

Circumference of a square = side length ×4 = 4a

Circumference = π× diameter =πd =π× radius× 2 = 2π r

Region:

Area of rectangle = length× width S = ab

Area of a square = side length × side length S = a?

Area of triangle = base × height ÷2 S=ah÷2.

Area of parallelogram = base × height S=ah

Trapezoidal area = (upper bottom+lower bottom) × height ÷2 S=(a+b)h÷2.

Diameter = radius× 2d = 2r

Radius = diameter ÷2 r=d÷2

Formula related to circle:

1, circular area: S=πr? ，S=π(d/2)？ . (d is the diameter and r is the radius).

2. area of semicircle: s semicircle = (π r 2)/2. (r is the radius).

3. Ring area: s great circle -S small circle = π (r 2-r 2) (r is the radius of great circle and r is the radius of small circle).

4. Circumference: C=2πr or c = π d..(d is the diameter and r is the radius).

5. The circumference of a semicircle: d+(πd)/2 or d+π r (d is the diameter and r is the radius).

6. The area of the circle where the sector is located is divided by 360 and multiplied by the angle n of the central angle of the sector, as shown below:

S=n/360×πr？ .

S=πr？ ×L/2πr=Lr/2(L is arc length and r is sector radius).