Equal sign

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Mathematical signs
Plus sign +
Minus sign - , ./.
Mark , ×
Divided sign : , ÷ , /
Plus minus sign ± ,
Comparison sign < , , = , , >
Root sign
Percent sign %
Sum symbol Σ
Product mark Π
Difference sign , Nabla ,
Partial differential
Integral sign
Concatenation characters
Infinity symbol
Angle sign , , ,
Vertical , parallel ,
Triangle , square ,
Diameter sign
Set theory
Union , cut ,
Difference , complement ,
Element character
Subset , superset , , ,
Empty set
Follow arrow , ,
Universal quantifier
Existential quantifier
Conjunction , disjunction ,
Negation sign ¬

In mathematics , formal logic and in the exact natural sciences , the equal sign ( = , also called is-equal sign ) stands between two expressions with the same value .


Introduction of the equal sign 1557, followed by “14x + 15 = 71” as the first printed equation

In ancient and medieval mathematics, the equality of two expressions was still literally written down (e.g. est egale for "is equal"). Descartes (1596–1650) shortened this with a æ (for Latin aequalis ) rotated by 180 ° , with the horizontal line being more and more omitted in the subsequent period. This symbol survived in the form as one of the proportionality symbols . As the founder of modern equal sign the Welsh mathematician applies Robert Recorde (1510-1558) with his book The Whetstone of Witte , dt (1557). The whetstone of knowledge . He justified the two parallel lines for an equality symbol with the early New English sentence … bicause noe.2.thynges, can be moare equalle. (Today's English: because no two things can be more equal , " because no two things can be the same").

The =, which was already used in England , was probably first introduced on the European continent by Gottfried Wilhelm Leibniz (1646–1716).


The equal sign is coded in ASCII with 61 ( decimal ), so as Unicode U + 003D (61 decimal = 3D hexadecimal ). It is not one of the named entities in markup languages , but can be replaced with &#61;or in HTML &#x3D;.


General use

The glyph = is generally used to represent facts of correspondence, equality or identity , in mathematics, computer science and technology also the assignment in the sense of a subsequent equal use.

The equal sign is often used as a substitute for the double hyphen ⹀ (U + 2E40) or its Japanese variant (U + 30A0).

In electrical engineering , the equal sign is used to identify direct voltage .

The equal sign and its variations

There are also modified forms with a different meaning, such as B. the equivalent sign (≙) or the rounding sign ( ≈) with the meaning approximately equal / rounded . If the inequality of two numbers is to be shown, a crossed out equal sign (≠) is used. A shape with three horizontal bars (≡) is used to indicate the identity of two arithmetic expressions.

The modifications: = or =: are used in mathematics to represent a definition of one side by the other side. The colons are always next to the object to be defined. The ≡ previously used for this should no longer be used in this sense ( DIN 1302 ), but shapes such as    (DIN 1302) or     ( ISO 31 -11) are possible.

For example, the set A can be defined as follows:

In programming languages that are derived from C , the (simple) equal sign is used for value assignment . In these languages, however, a double equal sign ( == ) is usually used as the comparison operator . In Fortran is used for the comparison operator. In languages ​​of the Pascal family, on the other hand, a: = is used for the assignment (in the predecessor Algol 60 this character combination or also a "←") and the equal sign as a comparison operator. There are also languages ​​such as B. BASIC , in which it is always clear from the context whether it is an assignment or a comparison and therefore use the equal sign for both the assignment and the comparison operator. .EQ.

Inequality sign

Since the character for inequality ≠ is not available in the ASCII character set, various programming languages ​​use digraphs such as <>(Pascal, BASIC), /=(Ada), !=( not equal , C, C ++) or ~=(ML); Fortran used .NE.(because of English n ot e qual , not equal ).

Mathematical equivalence signs
Z. Unicode meaning description Z. Unicode meaning description
= U+003D equal U+2260 unequal; not equal (1)
U+2261 congruent , identical U+2262 not congruent (1)
U+2250 Limit value approximation
U+2243 asymptotically equal U+2244 asymptotically unequal (1)
U+2242 Minus tildes
U+2245 approximately equal (Anglo-American,
according to DIN only permissible for asymptotically equal (≃))
U+2246 roughly, but not exactly the same
U+2247 neither roughly nor exactly the same
isomorphic , isomorphic in terms of category theory
U+224A about the same or equal
U+2248 roughly equal / rounded ( coll .: almost equal ) Double tilde U+2249 not about the same (coll .: not almost the same ) Crossed out double tildes
U+224B Triple tilde
U+2257 about the same
U+2252 roughly the same or picture U+2253 Picture or about the same
U+224C all the same
U+224D equivalent to
U+2263 exactly equivalent
U+224E geometrically equivalent
U+224F Difference between
U+2251 geometrically the same
U+225A equiangular
U+2254 results from (for definition on the left (: =) not provided) U+2255 does not result from (for definition on the right (= :) not provided)
U+225C right by definition
Definition on the left Colon + equal sign Right-hand definition Equal sign + colon
should be the same (for example in the introduction of evidence )
U+2259 corresponds
U+2258 corresponds to (unusual)
U+225E measured
U+225F maybe right away
U+225B Star is the same
U+2256 Circle in equal sign
(1) DIN 1302prescribes vertical strikethrough, but allows oblique strikethrough "if it is necessary for reasons of composition technology". ISO 31generally allows both forms.

See also

Wiktionary: Equal sign  - explanations of meanings, word origins, synonyms, translations

Individual evidence

  1. ... and written “is equal sign”; see also in the DWDS , under the equal sign , there also with "actual equal sign" (accessed on November 15, 2018)
  2. ^ Robert Recorde : The Whetstone of Witte . London 1557, p. 238.
  3. Matthias Helle: = . In: FU Berlin, Institute for Computer Science (Ed.): Seminar History of Mathematical Notation . 1999 (fu-berlin.de; script for the lecture on July 21, 1999).
  4. a b Hans Friedrich Ebel , Claus Bliefert , Walter Greulich : Writing and publishing in the natural sciences . Wiley-VCH, 2006, ISBN 978-3-527-30802-6 , 6.5.4 Frequently occurring special characters , p.  352 ff . ( limited preview in Google Book search).