1, additive commutative law

When two numbers are added, the positions of the two addends are exchanged and the sum remains unchanged, which is called additive commutative law. a+b=b+a

2. Additive associative law

When adding three numbers, add the first two numbers and then the third number, or add the last two numbers and then the first number, and the sum remains the same. This is the so-called law of additive association. a+b+c=(a+b)+c=a+(b+c)

3. The essence of subtraction

In subtraction, the minuend and the minuend add or subtract a number at the same time, and the difference remains the same. A-b=(a+c)-(b+c)ab=(a-c)-(b-c) In subtraction, how much the minuend increases or decreases, the minuend remains unchanged, and the difference increases or decreases. On the other hand, how much is reduced, how much is increased, the minuend is unchanged, and the difference increases or decreases with the decrease.

In subtraction, the subtropics are subtracted from the minuend, and these subtropics can be added, and the difference remains the same. a–b-c = a-(b+ c)

4. Multiplicative commutative law

Multiplication of numbers, where the positions of two factors are exchanged and the product remains unchanged, is called the commutative law of multiplication. a×b=b×a

5. Multiplicative associative law

Multiply three numbers, multiply the first two numbers and then the third number, or multiply the last two numbers and then the first number, and the product remains the same. This is the so-called law of multiplication and association. a×b×c=a×(b×c)

6. Law of Multiplication and Distribution

Multiplying the sum (or difference) of two numbers with a number is equivalent to multiplying these two numbers with this number respectively, and then adding (or subtracting) the two products. This is the so-called law of multiplication and division. (a+b)×c=a×c+b×c(a-b)×c=a×c-b×c

Expansion and supplement

Regular memory method: observing the formula table of addition, subtraction, multiplication and division, we can find some rules, for example, each row and column has a certain increase or decrease law. We can use these rules to remember, such as remembering the numbers in the first row and column, and then gradually expanding to other rows and columns.

For some complicated formulas, we can break them down into several parts for memory. For example, when memorizing multiplication formulas, we can decompose each multiplication formula into two addition formulas, which is easier to understand and remember.

Apply the formula of addition, subtraction, multiplication and division to real life, and deepen memory by solving practical problems. For example, when shopping, we can use the formula of addition, subtraction, multiplication and division to calculate the change and balance; When arranging time, we can use the formulas of addition, subtraction, multiplication and division to calculate the time difference and the distribution of time, and so on.