In mathematics, a multiplicative inverse or reciprocal for a number "x", denoted by 1/"x" or "x"−1, is a number which when multiplied by "x" yields the multiplicative identity, 1. The multiplicative inverse of a fraction "a"/"b" is "b"/"a". For the multiplicative inverse of a real number, divide 1 by the number. For example, the reciprocal of 5 is one fifth (1/5 or 0.2), and the reciprocal of 0.25 is 1 divided by 0.25, or 4. The reciprocal function, the function "f"("x") that maps "x" to 1/"x", is one of the simplest examples of a function which is its own inverse (an involution).