The additive inverse of an expression is the value that, when added to the original expression, results in zero.

For the expression $-a$, the additive inverse would be $a$. This is because:

$- a + a = 0$

So, the additive inverse of $-a$ is $a$.

Would you like more details on additive inverses or other concepts related to this?

Here are some related questions to explore:

1. What is the additive inverse of a number like 5 or -7?
2. How does the additive inverse relate to solving equations?
3. Can the concept of additive inverse be applied to matrices or vectors?
4. What happens when you add a number and its additive inverse?
5. How do you find the additive inverse of a polynomial?

Tip: To find the additive inverse of any number or expression, just change the sign!