The additive inverse of a number is a number, that when added to the original number, results in 0. So, basically, the additive inverse is the opposite...another words, it is the same number with a different sign
5....the additive inverse is -5....because 5 - 5 = 0
-2...the additive inverse is 2....because -2 + 2 = 0
1/3....the additive inverse is -1/3.....1/3 - 1/3 = 0