Multiplication sign facts for kids
×  

Multiplication sign


The multiplication sign, also known as the times sign or the dimension sign, is the symbol ×. While similar to a lowercase X, the form is properly a rotationally symmetric saltire.
Uses
In mathematics, the symbol × has a number of uses, including
 Multiplication of two scalar numbers, where it is read as "times" or "multiplied by"
 Cross product of two vectors, where it is usually read as "cross"
 Cartesian product of two sets, where it is usually read as "cross"
 Geometric dimension of an object, such as noting that a room is 10 feet × 12 feet in area, where it is usually read as "by" (for example: "10 feet by 12 feet")
 Dimensions of a matrix, where it is usually read as "by"
 A statistical interaction between two explanatory variables, where it is usually read as "by"
In biology, the multiplication sign is used in a botanical hybrid name, for instance Ceanothus papillosus × impressus (a hybrid between C. papillosus and C. impressus) or Crocosmia × crocosmiiflora (a hybrid between two other species of Crocosmia). However, the communication of these hybrid names with a standard nonmultiplication "x" is common when the actual "×" symbol is not readily available.
The multiplication sign is also used by historians for an event between two dates. When employed between two dates, for example 1225 and 1232, 1225×1232 means "no earlier than 1225 and no later than 1232". It can also be used in a date range: 1225×1232–1278.
History
The multiplication sign (×), often attributed to William Oughtred (who first used it in an appendix to the 1618 edition of John Napier's Mirifici Logarithmorum Canonis Descriptio), apparently had been in occasional use since the mid 16th century.
Similar notations
The letter "x" is sometimes used in place of the multiplication sign. This is considered incorrect in mathematical writing.
In algebraic notation, widely used in mathematics, a multiplication symbol is usually omitted wherever it would not cause confusion: "a multiplied by b" can be written as ab or a b.
Other symbols can also be used to denote multiplication, often to reduce confusion between the multiplication sign × and the commonly used variable x.
The standard numeric keypad, has the arithmetic operations of addition, subtraction, multiplication, and division represented by the +, , *, and / keys, respectively.