The negative sign of a positive number is-(negative sign, that is, negative sign).

The opposite sign of a negative number is+(plus sign, that is, plus sign).

"Add or subtract" means positive or negative, and symbols can be used to represent the positive or negative of rational numbers, or to add and subtract logarithms in four operations. Symbol is not a single concept in middle school physics. Some symbols are equivalent to rational numbers in mathematics, while others are used to express the nature and direction of physical quantities. The situation is more complicated.

The nature of reciprocal

1. Antique features: If A and B are inverse numbers, A+B = 0; Otherwise, if a+b=0, a and b are inverse numbers.

The reciprocal of zero is 0.

3. Antiquities appear in pairs and cannot appear alone.

4. Distinguish between "opposite numbers" and "quantities with opposite meanings". "Inverse number" is not only the opposite sign of a number, but also the numbers after the sign must be the same, such as +5 and -5, while "quantities with opposite meanings" only need the opposite sign, such as +3 and -7.

5. To ask the reciprocal of a number, just add a negative sign in front of the number. If the original number is signed (whether positive or negative), it should be put in parentheses first.