Additive Inverse
For any real number a, the number 2a is the additive inverse of a.
Change the sign of a number to get its additive inverse. The sum of a number
and its additive inverse is always 0.
The symbol “-” can be used to indicate any of the following:
a. a negative number, such as -9 or -15;
b. the additive inverse of a number, as in “- 4 is the additive inverse of 4”;
c. subtraction, as in 12 – 3.
In the expression – (-5), the symbol “-” is being used in two ways: the
first – indicates the additive inverse of -5, and the second indicates a negative
number, -5. Since the additive inverse of – 5 is 5, then – (- 5) = 5. This
example suggests the following property.
For any real number a, – (– a) = a.