RWM101: Foundations of Real World Math

You also need to be able to subtract negative numbers comfortably. If you consider negative numbers as debts, then you remove a debt when you subtract a negative number. Removing a debt of 4 dollars is like being given 4 dollars. This explains why the equation $5-(-4)=5+4$ holds: subtracting negative four is the same as adding positive four.

The symbols $-(-4)$ also represent the additive inverse OF (the additive inverse of $4$). Our work with additive inverses can help you write this expression in a different and simpler way. After all, the additive inverse of $4$ is $-4$, and now the additive inverse of $-4$ is, by definition, a number that results in zero when added to $-4$. Of course, the additive inverse of $-4$ is $4$ itself. All of this tells us that $-(-4)=4$. In the next section we will discuss multiplying and dividing negative numbers.

Watch this video for more examples on how to subtract negative numbers.