What is the additive inverse of -9?

The additive inverse of a number is a number that, when added to the original number, yields a sum of zero. In other words, it "cancels out" the original number.

The additive inverse of -9 would be a number that, when added to -9, equals zero. Therefore, the additive inverse of -9 is 9, because -9 + 9 = 0.