What is the distance between

-a and a?

the distance is 2·|a|

Step-by-step explanation:

The distance from "a" to the origin is |a|. And, the distance from the origin to - a is the same distance, so the distance between - a and a is ...

2·|a|

(This is true in any one-, two-, or three-dimensional Euclidean geometry we usually study.)