The multiplication sign (), also known as the times sign or the dimension sign, is a mathematical symbol used to denote the operation of multiplication, which results in a product.
The symbol is also used in botany, in botanical hybrid names.
The form is properly a four-fold rotationally symmetric saltire. The multiplication sign is similar to a lowercase X ().
History
The earliest known use of the symbol to indicate multiplication appears in an anonymous appendix to the 1618 edition of John Napier's . </blockquote>
Other works have been identified in which crossed diagonals appear in diagrams involving multiplied numbers, such as Robert Recorde's The Ground of Arts and Oswald Schreckenfuchs's 1551 edition of Almagest, but these are not symbolizations.
Uses
In mathematics, the symbol × has a number of uses, including
- Multiplication of two numbers, where it is read as "times" or "multiplied by"
- 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" (e.g., "10 feet by 12 feet")
- Display resolution in pixels, such as 1920 pixels across × 1080 pixels down. Read as "by".
- 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"
- the optical magnification is sometimes referred to as "power" (for example "10× power")
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 Latin letter "x" is common, especially 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 the expression "1225×1232" means "no earlier than 1225 and no later than 1232".
A monadic symbol is used by the APL programming language to denote the sign function.
Similar notations
The lower-case Latin letter 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: " multiplied by " can be written as or .