# Is there a word for opposite numbers?

Example: -100 and +100 - is there a way of describing the relationship between these numbers?

Obviously, I've already come up with "opposite", is there anything else?

This is for use in an email.

Example usage:

There's an issue with records that contain values that are opposite values of each other, -100 and +100

• -100 is the negative of +100. Commented May 2, 2015 at 17:04

In a less technical context, you could just call them negatives of each other.

Similarly, `5` and `1/5` are multiplicative inverses.

• Wow. I think I'll stick with "opposite" for this email then. Commented May 1, 2015 at 23:21
• I thought you were looking for the technical term. If it's casual email, try negative. Commented May 1, 2015 at 23:23
• Thanks. How would you phrase it though? "There's an issue with records that are negatives of each other"? Commented May 1, 2015 at 23:25
• Yes, something like that would be fine. If you said opposites, I'm not sure they would understand that you refer to the number values. Commented May 1, 2015 at 23:26
• `5` and `1/5` are also commonly called reciprocals, although that's not as precise. Commented May 2, 2015 at 5:13

This is hardly mainstream English, but there is a term.

The identity element under addition for the set of reals (or the set of integers) is zero;

x + 0 = 0 + x = x

The element that must be added to any element to give the identity element as the product (the general term for result of a binary operation; here the sum) is, for addition, known as the additive inverse of that element (number).

• Is there a better place for this type of question since it's not mainstream? Commented May 1, 2015 at 23:22
• The domain involved is maths, so the relevant SE website, or most other maths websites. Commented May 1, 2015 at 23:27
• Good to know - thanks. I probably should've elaborated on my intent though. Commented May 1, 2015 at 23:33

As noted by Barmar, additive inverse is the technically correct term, but in your context, you could use the following phrase:

There's an issue with records that contain values that differ only in their sign. For example, -100 and +100.

You could also say:

There's an issue with records that contain values that have equal magnitude but opposite sign. For example, -100 and +100.

I have read both these in various textbooks written by American authors. You could pick one of these alternatives, or a similar variant, depending on your audience.