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Obelus

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Obelus

÷
Obelus

An obelus (symbol: ÷, plural: obeluses or obeli) is a symbol consisting of a short horizontal line with a dot above and below. It is mainly used to represent the mathematical operation of division. It is therefore commonly called the division sign. Division may also be indicated by a horizontal line (fraction bar), or a slash.

Historically, this symbol had also been used to represent subtraction in Northern Europe.[1]

Contents

  • History 1
  • In computer systems 2
  • See also 3
  • Notes 4
  • External links 5

History

Plus and minuses. The obelus—or division sign—used as a variant of the minus sign in an excerpt from an official Norwegian trading statement form called «Næringsoppgave 1» for the taxation year 2010.

The word "obelus" comes from ὀβελός, the Ancient Greek word for a sharpened stick, spit, or pointed pillar. This is the same root as that of the word "obelisk". Originally this sign (or a plain line) was used in ancient manuscripts to mark passages that were suspected of being corrupted or spurious. The dagger symbol, also called an obelisk, is derived from the obelus and continues to be used for this purpose.

The obelus, invented by Aristarchus to mark suspected passages in Homer, is frequent in manuscripts of the [2]

Although previously used for subtraction, the obelus was first used as a symbol for division in 1659 in the algebra book Teutsche Algebra by Johann Rahn. Some think that John Pell, who edited the book, may have been responsible for this use of the symbol. The usage of the obelus to represent subtraction continued in some parts of Europe (including Norway and, until fairly recently, Denmark).[1] Other symbols for division include the slash or solidus (/), and the fraction bar (the horizontal bar in a vertical fraction).

In computer systems

In Microsoft Windows, the obelus is produced with Alt+0247 on the number pad or by pressing Alt Gr+ Shift++ when an appropriate keyboard layout is in use. In Mac OS, it is produced with ⌥ Option+/.

On UNIX-based systems using Screen or X with a Compose key enabled, it can be produced by composing : (colon) and - (hyphen/minus), though this is locale- and setting-dependent. It may also be input by Unicode code-point on GTK-based applications by pressing Control+ Shift+U, followed by the codepoint in hexadecimal (F7) and terminated by return.

In the Unicode character set, the obelus is known as the "division sign" and has the code point U+00F7.[3] In HTML, it can be encoded as ÷ or ÷ (at HTML level 3.2), or as ÷.

In LaTeX, the obelus is obtained by \div.

See also

Notes

  1. ^ a b  . Reprint of 1928 edition.
  2. ^ Burnett Hillman Streeter, The Four Gospels, London, Macmillan, 1924 [2]   The Aristarchus referred to was presumably Aristarchus of Samothrace.
  3. ^ Korpela, Jukka (2006), Unicode Explained: Internationalize documents, programs, and web sites, O'Reilly Media, Inc., p. 397,  .

External links

  • Earliest Uses of Various Mathematical SymbolsJeff Miller:
  • Where our arithmetic symbols come fromMichael Quinion:
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