convert negative numbers to positive, and back again.

I have two input values that I'm never sure if they're going to be negative or positive.
However I need to perform an operation on them (constantly) to impact a third value. This operation needs them to be both positive.
How do I convert the two incoming numbers to positive, operate on them, and then restore them to negative, and use them again as they were, regardless of whether or not they come into me as positive or negative?

@Deeeds to convert to a positive you could multiply the number by itself and then square root it, or for slightly better performance, multiply by 1 if its less than 0 and use a set input field. You should be able to still use the original value after.