① Add two numbers with the same symbol, take the same symbol, and add the absolute values.

(2) Sum two numbers with different absolute values, take the sign of the addend with larger absolute value, and subtract the number with smaller absolute value from the number with larger absolute value; The sum of two opposite numbers is 0.

③ A number with 0 still gets this number.

The subtraction rule of rational numbers:

Subtracting a number is equal to adding its reciprocal.

Rational number multiplication rule:

Multiply two numbers, the same sign is positive, the different sign is negative, and then multiply by the absolute value.

Any number multiplied by 0 is 0.

Rational number division rule:

① Divide two numbers, the same sign is positive and the different sign is negative, and divide by the absolute value.

Divide 0 by any number that is not equal to 0 to get 0.

(2) dividing by a number that is not equal to 0 is equal to multiplying the reciprocal of this number.

Additive commutative law;

When two numbers are added, the positions of the addend are exchanged and the sum is unchanged.

Additive associative law:

Add three numbers, first add the first two numbers, or add the last two numbers first, and the sum remains the same.

Multiplicative commutative law;

When two numbers are multiplied, the position of the exchange factor remains unchanged.

Distribution law:

Multiplying a number by the sum of two numbers is equivalent to multiplying this number by these two numbers respectively, and then adding the products.

The letter means: (a+b) c = AC+BC.

(A, B and C represent any rational number)

Operation order of rational numbers

(1) Multiply first, then divide, then add and subtract.

(2) Operation at the same level, from left to right.

(3) If there are brackets, do the operation in brackets first, and then follow the brackets, brackets and braces in turn.