1, additive commutative law: a+b=b+a two addend exchange positions, and the sum remains unchanged, which is called additive commutative law.

2, the law of addition and association: (A+B)+C = A+(B+C) Add the first two numbers or add the last two numbers first, and the sum is unchanged. This is the so-called law of addition and association.

3. Multiplicative commutative law: a×b=b×a commutates the positions of two factors, and the product remains unchanged. This is the so-called multiplication commutative law.

4. Multiplication and association law: (a×b)×c=a×(b×c) or a×b×c=a×(b×c) Multiply the first two numbers or multiply the last two numbers first, and the product remains unchanged. This is the so-called multiplicative associative law.

5. Multiplication distribution law: (a+b)×c=a×c+b×c or (a-b)×c=a×c-b×c The inverse application of multiplication distribution law: a×c+a×b=(a+b)×c or a× c-b× c =

6. In the mixed operation of addition and subtraction, the positions of subtraction and addend can be interchanged. However, when exchanging positions, you must "move" with the previous operation symbols, and the operation result will not change. Namely: a-(b-c) = a-b+c; a-(b+c)=a-b-c7 .