Add two numbers with the same sign, take the same sign, and add the absolute values a+b=+(a+b) and -a-b=-(a+b).

Two numbers with different signs are added, and when the absolute values are equal, the sum is 0; When the absolute values are not equal, take the sign of the addend with the larger absolute value and subtract the smaller absolute value from the larger absolute value.

When a number is added to 0, you still get this number.

Law of rational number subtraction

Subtracting a number is equal to adding the reciprocal of this number.

a-b=a+(-b)