“Inverses” in algebra are operations (or numbers) that “undo” each other. For example, if one multiplies 4 times its inverse, or 1/4, the solution is 1; thus, the rule for multiplicative inverse for x (with x ≠ 0) is 1/x, as in x(1/x) = 1. In addition, if you add -4 to 4, you get zero (0); thus, the additive inverse of x is -x, as in x + (-x) = 0.