In mathematics, an identity is an equality relating one mathematical expression A to another mathematical expression B, such that A and B (which might contain some variables) produce the same value for all values of the variables within a certain domain of discourse.[1][2] In other words, A = B is an identity if A and B define the same functions, and an identity is an equality between functions that are differently defined. For example, ( a + b ) 2 = a 2 + 2 a b + b 2 {\displaystyle (a+b)^{2}=a^{2}+2ab+b^{2}} and cos 2 --> θ θ --> + sin 2 --> θ θ --> = 1 {\displaystyle \cos ^{2}\theta +\sin ^{2}\theta =1} are identities.[3] Identities are sometimes indicated by the triple bar symbol ≡ instead of =, the equals sign.[4] Formally, an identity is a universally quantified equality.
Certain identities, such as a + 0 = a {\displaystyle a+0=a} and a + ( − − --> a ) = 0 {\displaystyle a+(-a)=0} , form the basis of algebra,[5] while other identities, such as ( a + b ) 2 = a 2 + 2 a b + b 2 {\displaystyle (a+b)^{2}=a^{2}+2ab+b^{2}} and a 2 − − --> b 2 = ( a + b ) ( a − − --> b ) {\displaystyle a^{2}-b^{2}=(a+b)(a-b)} , can be useful in simplifying algebraic expressions and expanding them.[6]
Geometrically, trigonometric identities are identities involving certain functions of one or more angles.[7] They are distinct from triangle identities, which are identities involving both angles and side lengths of a triangle. Only the former are covered in this article.
These identities are useful whenever expressions involving trigonometric functions need to be simplified. Another important application is the integration of non-trigonometric functions: a common technique which involves first using the substitution rule with a trigonometric function, and then simplifying the resulting integral with a trigonometric identity.
One of the most prominent examples of trigonometric identities involves the equation sin 2 --> θ θ --> + cos 2 --> θ θ --> = 1 , {\displaystyle \sin ^{2}\theta +\cos ^{2}\theta =1,} which is true for all real values of θ θ --> {\displaystyle \theta } . On the other hand, the equation
is only true for certain values of θ θ --> {\displaystyle \theta } , not all. For example, this equation is true when θ θ --> = 0 , {\displaystyle \theta =0,} but false when θ θ --> = 2 {\displaystyle \theta =2} .
Another group of trigonometric identities concerns the so-called addition/subtraction formulas (e.g. the double-angle identity sin --> ( 2 θ θ --> ) = 2 sin --> θ θ --> cos --> θ θ --> {\displaystyle \sin(2\theta )=2\sin \theta \cos \theta } , the addition formula for tan --> ( x + y ) {\displaystyle \tan(x+y)} ), which can be used to break down expressions of larger angles into those with smaller constituents.
The following identities hold for all integer exponents, provided that the base is non-zero:
Unlike addition and multiplication, exponentiation is not commutative. For example, 2 + 3 = 3 + 2 = 5 and 2 · 3 = 3 · 2 = 6, but 23 = 8 whereas 32 = 9.
Also unlike addition and multiplication, exponentiation is not associative either. For example, (2 + 3) + 4 = 2 + (3 + 4) = 9 and (2 · 3) · 4 = 2 · (3 · 4) = 24, but 23 to the 4 is 84 (or 4,096) whereas 2 to the 34 is 281 (or 2,417,851,639,229,258,349,412,352). When no parentheses are written, by convention the order is top-down, not bottom-up:
Several important formulas, sometimes called logarithmic identities or log laws, relate logarithms to one another:[a]
The logarithm of a product is the sum of the logarithms of the numbers being multiplied; the logarithm of the ratio of two numbers is the difference of the logarithms. The logarithm of the pth power of a number is p times the logarithm of the number itself; the logarithm of a pth root is the logarithm of the number divided by p. The following table lists these identities with examples. Each of the identities can be derived after substitution of the logarithm definitions x = b log b --> x , {\displaystyle x=b^{\log _{b}x},} and/or y = b log b --> y , {\displaystyle y=b^{\log _{b}y},} in the left hand sides.
The logarithm logb(x) can be computed from the logarithms of x and b with respect to an arbitrary base k using the following formula:
Typical scientific calculators calculate the logarithms to bases 10 and e.[8] Logarithms with respect to any base b can be determined using either of these two logarithms by the previous formula:
Given a number x and its logarithm logb(x) to an unknown base b, the base is given by:
The hyperbolic functions satisfy many identities, all of them similar in form to the trigonometric identities. In fact, Osborn's rule[9] states that one can convert any trigonometric identity into a hyperbolic identity by expanding it completely in terms of integer powers of sines and cosines, changing sine to sinh and cosine to cosh, and switching the sign of every term which contains a product of an even number of hyperbolic sines.[10]
The Gudermannian function gives a direct relationship between the trigonometric functions and the hyperbolic ones that does not involve complex numbers.
Formally, an identity is a true universally quantified formula of the form ∀ ∀ --> x 1 , … … --> , x n : s = t , {\displaystyle \forall x_{1},\ldots ,x_{n}:s=t,} where s and t are terms with no other free variables than x 1 , … … --> , x n . {\displaystyle x_{1},\ldots ,x_{n}.} The quantifier prefix ∀ ∀ --> x 1 , … … --> , x n {\displaystyle \forall x_{1},\ldots ,x_{n}} is often left implicit, when it is stated that the formula is an identity. For example, the axioms of a monoid are often given as the formulas
or, shortly,
So, these formulas are identities in every monoid. As for any equality, the formulas without quantifier are often called equations. In other words, an identity is an equation that is true for all values of the variables.[11][12]
Rap rockBeastie Boys di Club Citta Kawasaki, Jepang, dalam tur Check Your Head, 1992Sumber aliranHip hoprockSumber kebudayaanAwal ke pertengahan 1980an, Amerika SerikatAlat musik yang biasa digunakanRapgitar elektrikbassturntabledrummesin drumvokalsamplerpenyintesiskiborBentuk turunanCountry raphip hop alternatifSubgenreRap metalrapcoreTopik lainnyaEmo rapnu metal Rap rock adalah genre campuran yang memadukan unsur vokal dan instrumen hip hop dengan berbagai bentuk musik rok. Subgenre rap rock y…
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Willem Johannes Dominicus van Dijck kan verwijzen naar: Willem Johannes Dominicus van Dijck (1850-1909), secretaris prins Willem Alexander (1851-1884) Willem Johannes Dominicus van Dijck (1899-1969), bijzonder hoogleraar aan de Technische Universiteit Delft Willem Johannes Dominicus van Dijck (burgemeester), burgemeester van Goudswaard, Nieuw-Beijerland en Piershil en Maassluis Bekijk alle artikelen waarvan de titel begint met Willem Johannes Dominicus van Dijck of met Willem Johannes …
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Esta página cita fontes, mas que não cobrem todo o conteúdo. Ajude a inserir referências. Conteúdo não verificável pode ser removido.—Encontre fontes: ABW • CAPES • Google (N • L • A) (Outubro de 2010) A Pancor Jackhammer é uma espingarda calibre 12 automática a gás.[1] É uma das poucas espingardas automáticas e, embora patenteada em 1987, nunca entrou em produção em grande escala. Apenas alguns protótipos do Jackha…
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This article relies excessively on references to primary sources. Please improve this article by adding secondary or tertiary sources. Find sources: Grand Central Partnership – news · newspapers · books · scholar · JSTOR (November 2008) (Learn how and when to remove this template message) Grand Central PartnershipFounded1985[1]FocusThe care of the Business Improvement District surrounding Grand Central Terminal stretching, roughly, from 35th to 54…
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