1. The circumference of the rectangle = (length+width) ×2, and C=(a+b)×2.
Second, the perimeter of the square = side length ×4, C=4a.
Third, the area of a rectangle = length × width, and S=ab.
4. Square area = side length × side length, S = a.a = a 2.
V area of triangle = base × height ÷2, S=ah÷2.
Six, parallelogram area = bottom x height, S=ah.
Seven, trapezoidal area = (upper bottom+lower bottom) × height ÷2, s = (a+b) H ÷ 2.
Eight, circumference = pi× diameter = pi× radius× 2, c=πd=2π.