Root sign
√



Mathematical signs  
arithmetic  
Plus sign  + 
Minus sign   , ./. 
Mark  ⋅ , × 
Divided sign  : , ÷ , / 
Plus minus sign  ± , ∓ 
Comparison sign  < , ≤ , = , ≥ , > 
Root sign  √ 
Percent sign  % 
Analysis  
Sum symbol  Σ 
Product mark  Π 
Difference sign , Nabla  ∆ , ∇ 
Prime  ′ 
Partial differential  ∂ 
Integral sign  ∫ 
Concatenation characters  ∘ 
Infinity symbol  ∞ 
geometry  
Angle sign  ∠ , ∡ , ∢ , ∟ 
Vertical , parallel  ⊥ , ∥ 
Triangle , square  △ , □ 
Diameter sign  ⌀ 
Set theory  
Union , cut  ∪ , ∩ 
Difference , complement  ∖ , ∁ 
Element character  ∈ 
Subset , superset  ⊂ , ⊆ , ⊇ , ⊃ 
Empty set  ∅ 
logic  
Follow arrow  ⇒ , ⇔ , ⇐ 
Universal quantifier  ∀ 
Existential quantifier  ∃ 
Conjunction , disjunction  ∧ , ∨ 
Negation sign  ¬ 
The root sign (√) is the symbol used in mathematical notation for the square root of a number or for the square root . By specifying a root exponent, roots with any exponent, such as cube roots , are noted with the help of the root symbol .
history
The root sign √ probably comes from the small letter r and stands for square root. An alternative origin is a point with a decorative spread, comparable to a quarter note. It was first used in 1525 by the German mathematician Christoph Rudolff . The extension of the r over the full term  the Vinculum  was introduced in 1637 in the book Discours de la méthode by Descartes . The hieroglyph for the square root in ancient Egypt is a right angle. This notation is used in the Lahunpapyri .
Traditions of the formula set
The different traditions of the formula set reveal the abovementioned origin more or less clearly. The shape of the root symbol in the American formula shows little resemblance to the small r . In particular, the oblique downward stroke on the left side of the character distinguishes it from the form in other traditions of the formula set. Depending on its size, the root sign shows slightly different variants, as can be seen in the following formula:
The root sign in the German and Russian formula sets, however, always shows the same shape regardless of size. The German form of the root sign is very similar to the lowercase letter r . However, the stroke on the left does not necessarily have the same height as the stroke above the radicand, as shown in the picture German form of the root sign , so that the transition to the Russian form is fluid. The root sign in the Russian set of formulas shows a form that has properties of both the German and the American form.
German form of the root symbol, typically used in DIN standards
Web typographic representation
Problems with this special character arise in the electronic representation, because it can usually not be entered directly via the keyboard. If the root symbol is entered as a character in Unicode or HTML , the problem arises that the radicand is not "below" the root because the letter set does not allow the root character to be extended in a meaningful way.
character  Unicode  designation  HTML  Latex  

position  designation  hexadecimal  decimal  named  
√ 
U+221A

square root  square root  & # x221a;  & # 8730;  ? 
\sqrt

∛ 
U+221B

cube root  Cube root  & # x221b;  & # 8731; 
\sqrt[3]


∜ 
U+221C

fourth root  Fourth root  & # x221c;  & # 8732; 
\sqrt[4]

literature
 Ulrich Felgner: About the origin of the root sign. In: Mathematical semester reports. Vol. 52, No. 1, 2005, Springer, pp. 1–7, ISSN 0720728X ( doi : 10.1007 / s0059100400834 )
 Florian Cajori: A History of Mathematical Notations (Two Volume in One) , Cosimo, 2011 (reprint). ISBN 1616405716 .
Web links
Individual evidence
 ^ Cajori, p. 375.
 ↑ According to information from DIN, Standards Committee Technical Basics, in Aug. 2010, details are not specified. This representation is a combination of many similar representations in the standards.
 ↑ Valentin Zaitsev, Andrew Janishewsky, Alexander Berdnikov: Russian Typographical Traditions in Mathematical Literature . In: EuroTeX'99 proceedings. ( Memento of September 28, 2012 in the Internet Archive ) (PDF 196 kB, English).