1, circle: C=πd=2πr (d is diameter, r is radius, π).

2. The perimeter of the triangle is C = a+b+c(abc is three sides of the triangle).

3. Quadrilateral: C=a+b+c+d(abcd is the side length of quadrilateral)

4. Special: rectangle: C=2(a+b) (a is long and B is wide)

5. Square: C=4a(a is the side length of the square)

Three-level area calculation formula:

1, rectangular area = length× width S=ab

2. Area of a square = side length × side length S = a× a.

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

4. parallelogram area = bottom x height S=ah.

5. trapezoidal area = (upper bottom+lower bottom) × height ÷ 2s = (a+b) h ÷ 2.