All integers (negative, zero and positive) are divided into 2 sets, male and female; none of those sets is an empty set.

Let:
male number + female number = male number
male number * female number = female number

Given the above, for each of the following equations specify whether the result Ri is a female number, a male number, or could be either:

R1= female number * female number
R2= female number + female number
R3 = male number * male number
R4= male number + male number

Please justify your decisions.