In mathematics, the reciprocal (or multiplicative inverse) of a number is 1 divided by the number, or equivalently, the number raised to the power of -1 (as in \displaystyle{ \tfrac{1}{x} } and \displaystyle{ x^{-1} }). All numbers have a reciprocal except zero, since no number times 0 is 1. Two numbers are reciprocal of each other if and only if their product is 1. For example:

• 2.5 and 0.4 are reciprocals, because 2.5 × 0.4 = 1.
• -0.2 and -5 are reciprocals, because -0.2 × -5 = 1.
• 1 and -1 are their own reciprocals, because 1 × 1 = 1 and -1 × -1 = 1.