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### Arithmetic number

In historical documents, **arithmetic numbers** are mentioned. It is a vague concept, because it only says you can calculate with them.

##### Explanation

Usually positive numbers and the number zero are meant. Sometimes, however, it is just about the real numbers.

##### Example 1

Roots of negative numbers should be converted with the definition of the imaginary unit *i*^{2} = −1 . Then you don't have a minus sign anymore, and you can calculate the root. When multiplying, you get

It produces a negative number, and you probably wouldn't have expected that.