First of all, it doesn't make much sense to ask any questions alone.

Why? We might as well review the topics we have done before and show senior high school students the topics in junior high school. Many of them are wrong (although they were right in junior high school). Similarly, I think the landlord's problem is a dead end. The landlord may wish to ask all the problems encountered and discuss them together.

I want to tell the questioner that any question, any question in the formal exam, is within a certain range or by default. For example, all questions in primary school papers are positive integers, zeros and scores by default. The calculation of junior high school is within the real number range.

-Is 2 a multiple of 2? I promise I won't get caught in the final exam in any year.

If in primary school, is -2 a multiple of 2? Obviously not, because the default definition of primary school is within the range of positive integer 0.

So, there is no need to ask this question. If you have to ask, you should solve it like this.

The definition of multiple is learned in primary school, and the definition of multiple has not been re-learned in junior high school, senior high school and university. Third, negative numbers have gone beyond the default concept of primary schools. Can you think that -2 is a multiple of 2? This statement is wrong.

Fourth, it can also be said that it is correct. Many theorems in mathematics can be generalized, and if you insist on extending the concept of multiple to negative numbers, it is also possible.

I have come to a conclusion about your other question, so I suggest you forget it. After all, this is actually not a question worth discussing. In mathematics, definition is the easiest to change. This artificial definition is different for everyone. Although I give you a strict proof, it may change because a famous person has a definite definition one day. After all, this definition is not very important.