Division by two

In mathematics, division by two, also called halving, mediation, or dimidiation, is common in formulas and as a step in arithmetical calculations; it is equivalent to multiplication by one half. Starting with an arbitrary number or quantity ⁠${\displaystyle x}$⁠, its division by two can be written as any of the following equivalent expressions: $${\displaystyle x\div 2,\ x/2,\ {\frac {x}{2}},\ {\tfrac {1}{2}}x,\ 0.5x.}$$

The treatment of this as a different operation from multiplication and division by other numbers goes back to the ancient Egyptians, whose multiplication algorithm used division by two as one of its fundamental steps. Some mathematicians as late as the sixteenth century continued to view halving as a separate operation, and it often continues to be treated separately in modern computer programming. Performing this operation is simple in decimal arithmetic, in the binary numeral system used in computer programming, and in other even-numbered bases.