The Additive Inverse Axiom states that every real number has a unique additive inverse.
Zero is its own additive inverse. The sum of a number and the Additive Inverse of that number is zero.

Example:The additive inverse of x is -x and when they are added together their sum is zero. x + (-x) = 0

Example:The additive inverse of -12 is 12 and when they are added together their sum is zero. (-12) + 12 = 0