The Additive Inverse Property (Add  Inv):

The sum of any number and its additive inverse is always a zero. To find the additive inverse of a number is simply finding the opposite of that number. Notice: when you are finding the additive inverse of a number, you are finding a number that if you add it to the given number the answer will be a zero. The only way this will happen is if we add the opposite of the number. To find the additive inverse is to find the opposite.

Example:
Find the add Inv of the following numbers:

Notice: the sum is always zero.