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

3. Area of rectangle = length× width S=ab.

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

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

6. Area of parallelogram = base × height S=ah.

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

8. Diameter = radius ×2 d=2r Radius = diameter ÷2 r=d÷2.

9. The circumference of a circle = π× diameter = π× radius× 2c = π d = 2π r.

10, area of circle = π× radius× radius.

1 1, triangle area = base × height ÷2. The formula S=a×h÷2.

12, square area = side length × side length formula s = a× a.

13, area of rectangle = length× width formula s = a× b.

14, area of parallelogram = base× height formula s = a× h.

15, trapezoidal area = (upper bottom+lower bottom) × height ÷2 formula S=(a+b)h÷2.

16, sum of internal angles: sum of internal angles of triangle = 180 degrees.

17, cuboid volume = length× width× height formula: V=abh.

18, cuboid (or cube) volume = bottom area × height formula: V=abh.

19, volume of cube = side length × side length × side length formula: V=aaa.

20. The circumference of a circle = diameter × π formula: L = π d = 2π r.

2 1, area of circle = radius× radius× π formula: S=πr2.

22. Surface (side) area of cylinder: The surface (side) area of cylinder is equal to the perimeter of the bottom multiplied by the height. Formula: S=ch=πdh=2πrh.

23. Surface area of a cylinder: The surface area of a cylinder is equal to the perimeter of the bottom multiplied by the height plus the area of the circles at both ends. Formula: S=ch+2s=ch+2πr2.

24. Volume of cylinder: The volume of cylinder is equal to the bottom area multiplied by the height. Formula: V=Sh.

25. The volume of the cone = 1/3 bottom× product height. Formula: V= 1/3Sh.

26. Law of Fraction Addition and subtraction: Fraction addition and subtraction with denominator, only numerator addition and subtraction, denominator unchanged. Add and subtract fractions with different denominators, divide first and then add and subtract.

27. Multiplication of fractions: use the product of molecules as numerator and the product of denominator as denominator.

28. The law of division of fractions: dividing by a number is equal to multiplying the reciprocal of this number.