The product of two real numbers is 1, so these two numbers are reciprocal (the number here is the number of numbers, making four sounds; "Reverse" means to reverse the car. For example, the following sets of numbers are reciprocal:

3 and 1/3 5/3 and 3/5 -0.5 and -2.

In addition, the reciprocal of 1 and-1 is itself, because zero cannot be divisible, so zero has no reciprocal.

Supplement: In advanced mathematics, negative numbers also have reciprocal, for example, the reciprocal of I is -i(i is an imaginary unit, and the square of I is-1).

In addition, there is a saying of "negative reciprocal", that is, two numbers whose product is negative 1 are mutually "negative reciprocal".