1, the perimeter of the rectangle = (length+width) ×2, and C=(a+b)×2.

2. The circumference of a square = side length ×4, and C=4a.

3. The area of a rectangle = length × width, and S=ab.

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

5. The area of triangle = base × height ÷2, and S=ah÷2.

6. The area of parallelogram = base × height, and S=ah.

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

8. The circumference of a circle = pi× diameter = pi× radius× 2, and c=πd? =2πr .

9. Area of circle = π× radius× radius? πr^2。