 Plusminus sign

For other uses, see plusminus (disambiguation).±
The plusminus sign (±) is a mathematical symbol commonly used either
 to indicate the precision of an approximation, or
 to indicate a value that can be of either sign.
The sign is normally pronounced "plus or minus". In experimental sciences, the sign commonly indicates the confidence interval or error in a measurement, often the standard deviation or standard error. The sign may also represent an inclusive range of values that a reading might have. In mathematics, it may indicate two possible values: one positive, and one negative.
Contents
Precision indication
The use of ± for an approximation is most commonly encountered in presenting the numerical value of a quantity together with its tolerance or its statistical margin of error. For example, "5.7±0.2" denotes a quantity that is specified or estimated to be within 0.2 units of 5.7; it may be anywhere in the range from 5.7 − 0.2 (i.e., 5.5) to 5.7 + 0.2 (5.9). In scientific usage it sometimes refers to a probability of being within the stated interval, usually corresponding to either 1 or 2 standard deviations (a probability of 68.3% or 95.4% in a Normal distribution).
A percentage may also be used to indicate the error margin. For example, 230 ± 10% V refers to a voltage within 10% of either side of 230 V (207 V to 253 V). Separate values for the upper and lower bounds may also be used. For example, to indicate that a value is most likely 5.7 but may be as high as 5.9 or as low as 5.6, one could write 5.7+0.2
−0.1.Shorthand
In mathematical equations, the use of ± may be found as shorthand, to present two equations in one formula: + or −, represented with ±.
For example, given the equation x^{2} = 1, one may give the solution as x = ±1, such that both x = +1 and x = −1 are valid solutions.
More generally we have the quadratic formula:
If ax^{2} + bx + c = 0 then
Written out in full, this states that there are two solutions to the equation, i.e. that
Another example is found in the trigonometric identity
This stands for two identities: one with "+" on both sides of the equation, and one with "−" on both sides.
A somewhat different use is found in this presentation of the formula for the Taylor series of the sine function:
This mild abuse of notation is intended to indicate that the signs of the terms alternate, where (starting the count at 0) the terms with an even index n are added while those with an odd index are subtracted. A more rigorous presentation would use the expression (−1)^{n}, which gives +1 when n is even and −1 when n is odd.
Minusplus sign
There is another character, the minusplus sign (∓). It is generally used in conjunction with the "±" sign, in such expressions as "x ± y ∓ z", which can be interpreted as meaning "x + y − z" or/and "x − y + z", but not "x + y + z" nor "x − y − z". The upper "−" in "∓" is considered to be associated to the "+" of "±" (and similarly for the two lower symbols) even though there is no visual indication of the dependency. The original expression can be rewritten as "x ± (y − z)" to avoid confusion, but cases such as the trigonometric identity
are most neatly written using the "∓" sign. The trigonometric equation above thus represents the two equations:
but never
because the signs are exclusively alternating.
Other uses
± and ∓ are used in chess notation to denote an advantage for white and black respectively.
Encodings
 In ISO 88591, 7, 8, 9, 13, 15, and 16, the plusminus symbol is given by the code 0xB1_{hex} Since the first 256 code points of Unicode are identical to the contents of ISO88591 this symbol is also at Unicode code point U+00B1.
 The symbol also has a HTML entity representation of
±
.  On Windows systems, it may be entered by means of Alt codes, by holding the ALT key while typing the numbers 0177 on the numeric keypad.
 On Unixlike systems, it can be entered by typing the sequence compose + .
 On Macintosh systems, it may be entered by pressing option shift = (on the nonnumeric keypad).
 The rarer minusplus sign (∓) is not generally found in legacy encodings and does not have a named HTML entity but is available in Unicode with codepoint U+2213 and so can be used in HTML using
∓
or∓
.  In TeX 'plusorminus' and 'minusorplus' symbols are denoted
\pm
and\mp
, respectively.  These characters are also seen written as a (rather untidy) underlined or overlined + symbol. ( + or + ).
Similar characters
The plusminus sign resembles the Chinese character 士, whereas the minusplus sign resembles 干.
See also
References
Categories: Elementary arithmetic
 Mathematical symbols
Wikimedia Foundation. 2010.
Look at other dictionaries:
plus minus sign — plius minus ženklas statusas T sritis informatika apibrėžtis Ženklas ±. Kodai: 177 (ISO/IEC 8859 13, dešimtainis), U+00B1. Vartojamas skaičių intervalui nuo –n iki +n žymėti, pvz., ±0,1. atitikmenys: angl. plus minus sign … Enciklopedinis kompiuterijos žodynas
plus/minus sign — noun Date: 1971 the sign ± used to indicate a quantity (as 2 in “the square root of 4 is ±2”) taking on both an algebraically positive value and its negative and to indicate a plus or minus quantity (as 4 in “the population age was 30 ± 4 years”) … New Collegiate Dictionary
plusminus sign — noun the symbol ±, meaning plus or minus , used to indicate the precision of an approximation (as in The result is 10 ± 0.3 , meaning the result is somewhere between 10 0.3, that is, 9.7, and 10 + 0.3, that is, 10.3), or as a convenient shorthand … Wiktionary
Plusminus — or plus/minus (+/ ) may refer to:*Plus minus sign, a mathematical symbol (±) *Plus/minus, an ice hockey statistic *+/ , an American rock band … Wikipedia
plus/minus symbol — noun see plus/minus sign … New Collegiate Dictionary
minus sign — minus .sign also minus n a sign ( ) showing that a number is less than zero, or that the second of two numbers is to be ↑subtracted from the first →↑plus sign … Dictionary of contemporary English
Plus and minus signs — This article is about the mathematical symbols. For other uses of plus , see Plus (disambiguation). For other uses of minus , see Minus (disambiguation). The plus and minus signs (+ and −) are mathematical symbols used to represent the notions of … Wikipedia
minusplus sign — noun the symbol ∓, meaning minus or plus , used alongside the plus minus sign to show that a negative value is to be taken where the positive value is indicated by the plus minus sign, and vice versa (as in (x nbsp;± nbsp;1) nbsp;/ nbsp;(x nbsp;∓ … Wiktionary
minus — [mī′nəs] prep. [LME < L, less, neut. sing. of minor,MINOR] 1. reduced by the subtraction of; less [four minus two] 2. Informal without; lacking [minus a toe] adj. 1. indicating or involving subtraction [a minus sign] … English World dictionary
Minus (disambiguation) — Minus may refer to: Minus sign, a mathematical symbol; See Plus and minus signs minus is a Web based file hosting service m nus, a Canadian record label; See Minus (record label) Mínus, an Icelandic band Minus a song by Beck from Odelay Minus a… … Wikipedia