1. The circumference of a rectangle = (length+width) ×2, and C=(a+b)×2?

Second, the perimeter of the square = side length ×4, C=4a?

Third, the area of the rectangle = length × width, S=ab?

4. area of a square = side length × side length, S=a.a=? a^2

Verb (abbreviation of verb) 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 = π× diameter = π× radius× 2, c=πd? =2πr？

Nine, the area of the circle = π× radius× radius? πr ^2