Additive commutative law: A+B = B+A.
Additive associative law: (a+b)+c=a+(b+c)
Multiplicative commutative law: ab=ba
Law of multiplicative association: (ab)c=a(bc)
Multiplication and distribution law: a(b+c)=ab+ac.
Second, the geometric figure calculation formula
Perimeter: the length of a circle around an object.
① Rectangular perimeter = (length+width) ×2 C=(a+b)×2
② Square perimeter = side length ×4 C=4a
③ Circumference = pi× diameter = pi× radius× 2c = π dc = 2π r.
Area: the size of the surface or closed figure of an object.
① area of rectangle = length× width S=ab
② Area of a square = side length × side length S=a? a=a2
③ area of parallelogram = base × height S=ah
④ Area of triangle = base × height ÷2 S=ah÷2.
Third, the quantitative relationship.
1, number of copies × number of copies = total
Total copies/number of copies = number of copies
Total copies/number of copies = number of copies
2. Unit price × quantity = total price
Total price/unit price = quantity
Total price ÷ quantity = unit price
3. Speed × time = distance
Distance/speed = time
Distance/time = speed
Fourth, the algorithm of fractional multiplication:
1, the fraction times the integer, and the product of the multiplication of the numerator and the integer is the numerator, and the denominator remains the same.
2. Fractions are multiplied by fractions, the product of numerator multiplication is numerator, and the product of denominator multiplication is denominator.
Simplification of fractions: numerator and denominator are divided by their greatest common factor at the same time.
Five, fractional division
Fractional division is the inverse operation of fractional multiplication, that is, the operation of finding another factor by knowing the product of two numbers and one factor. Dividing by a number is the reciprocal of this number, and dividing by a few is the fraction of this number.
Ratio: The division of two numbers is also called the ratio of two numbers. The ratio represents the relationship between two numbers, which can be written in the form of ratio or expressed in fraction, but still read several ratios. Note: 10/2=5/ 1, indicating that the ratio is 5 1 and 19: 2 = 5, which is a ratio, and the ratio is a number, which can be an integer, a fraction or a decimal.