TheInfoList

In
mathematics Mathematics (from Ancient Greek, Greek: ) includes the study of such topics as quantity (number theory), mathematical structure, structure (algebra), space (geometry), and calculus, change (mathematical analysis, analysis). It has no generally ...
, a polynomial is an expression consisting of indeterminates (also called variables) and
coefficient In mathematics, a coefficient is a multiplicative factor in some Summand, term of a polynomial, a series (mathematics), series, or any expression (mathematics), expression; it is usually a number, but may be any expression (including variables suc ...
s, that involves only the operations of
addition Addition (usually signified by the plus symbol ) is one of the four basic operations of arithmetic Arithmetic (from the Ancient Greek, Greek wikt:en:ἀριθμός#Ancient Greek, ἀριθμός ''arithmos'', 'number' and wikt:en:τική#An ...
,
subtraction Subtraction is an arithmetic operation that represents the operation of removing objects from a collection. Subtraction is signified by the minus sign, . For example, in the adjacent picture, there are apples—meaning 5 apples with 2 taken awa ...

,
multiplication Multiplication (often denoted by the cross symbol , by the mid-line dot operator , by juxtaposition, or, on computers, by an asterisk ) is one of the four elementary Operation (mathematics), mathematical operations of arithmetic, with the ...

, and non-negative
integer An integer (from the Latin Latin (, or , ) is a classical language belonging to the Italic languages, Italic branch of the Indo-European languages. Latin was originally spoken in the area around Rome, known as Latium. Through the power of t ...
exponentiation Exponentiation is a mathematical operation, written as , involving two numbers, the '' base'' and the ''exponent'' or ''power'' , and pronounced as " raised to the power of ". When is a positive integer An integer (from the Latin wikt: ...
of variables. An example of a polynomial of a single indeterminate is . An example in three variables is . Polynomials appear in many areas of mathematics and science. For example, they are used to form
polynomial equation In mathematics Mathematics (from Ancient Greek, Greek: ) includes the study of such topics as quantity (number theory), mathematical structure, structure (algebra), space (geometry), and calculus, change (mathematical analysis, analysis). It h ...
s, which encode a wide range of problems, from elementary word problems to complicated scientific problems; they are used to define polynomial functions, which appear in settings ranging from basic
chemistry Chemistry is the science, scientific study of the properties and behavior of matter. It is a natural science that covers the Chemical element, elements that make up matter to the chemical compound, compounds composed of atoms, molecules and i ...
and
physics Physics is the natural science that studies matter, its Elementary particle, fundamental constituents, its Motion (physics), motion and behavior through Spacetime, space and time, and the related entities of energy and force. "Physical scien ...

to
economics Economics () is the social science that studies how people interact with value; in particular, the Production (economics), production, distribution (economics), distribution, and Consumption (economics), consumption of goods and services. ...
and
social science Social science is the Branches of science, branch of science devoted to the study of society, societies and the Social relation, relationships among individuals within those societies. The term was formerly used to refer to the field of sociol ...

; they are used in
calculus Calculus, originally called infinitesimal calculus or "the calculus of infinitesimal In mathematics, infinitesimals or infinitesimal numbers are quantities that are closer to zero than any standard real number, but are not zero. They do not ex ...
and
numerical analysis (c. 1800–1600 BC) with annotations. The approximation of the square root of 2 is four sexagesimal figures, which is about six decimal figures. 1 + 24/60 + 51/602 + 10/603 = 1.41421296... Numerical analysis is the study of algorithms that use num ...
to approximate other functions. In advanced mathematics, polynomials are used to construct
polynomial ring In mathematics Mathematics (from Ancient Greek, Greek: ) includes the study of such topics as quantity (number theory), mathematical structure, structure (algebra), space (geometry), and calculus, change (mathematical analysis, analysis). ...
s and
algebraic varieties Algebraic varieties are the central objects of study in algebraic geometry Algebraic geometry is a branch of mathematics, classically studying zero of a function, zeros of multivariate polynomials. Modern algebraic geometry is based on the us ...
, which are central concepts in
algebra Algebra (from ar, الجبر, lit=reunion of broken parts, bonesetting, translit=al-jabr) is one of the areas of mathematics, broad areas of mathematics, together with number theory, geometry and mathematical analysis, analysis. In its most ge ...
and
algebraic geometry Algebraic geometry is a branch of mathematics Mathematics (from Ancient Greek, Greek: ) includes the study of such topics as quantity (number theory), mathematical structure, structure (algebra), space (geometry), and calculus, change (ma ...
.

# Etymology

The word ''polynomial'' joins two diverse roots: the Greek ''poly'', meaning "many", and the Latin ''nomen'', or name. It was derived from the term '' binomial'' by replacing the Latin root ''bi-'' with the Greek ''poly-''. That is, it means a sum of many terms (many
monomial In mathematics, a monomial is, roughly speaking, a polynomial which has only one summand, term. Two definitions of a monomial may be encountered: # A monomial, also called power product, is a product of powers of Variable (mathematics), variables wi ...
s). The word ''polynomial'' was first used in the 17th century.

# Notation and terminology

The ''x'' occurring in a polynomial is commonly called a ''variable'' or an ''indeterminate''. When the polynomial is considered as an expression, ''x'' is a fixed symbol which does not have any value (its value is "indeterminate"). However, when one considers the
function Function or functionality may refer to: Computing * Function key A function key is a key on a computer A computer is a machine that can be programmed to carry out sequences of arithmetic or logical operations automatically. Modern comp ...
defined by the polynomial, then ''x'' represents the argument of the function, and is therefore called a "variable". Many authors use these two words interchangeably. It is common to use uppercase letters for indeterminates and corresponding lowercase letters for the variables (or arguments) of the associated function. A polynomial ''P'' in the indeterminate ''x'' is commonly denoted either as ''P'' or as ''P''(''x''). Formally, the name of the polynomial is ''P'', not ''P''(''x''), but the use of the
functional notation In mathematics Mathematics (from Ancient Greek, Greek: ) includes the study of such topics as quantity (number theory), mathematical structure, structure (algebra), space (geometry), and calculus, change (mathematical analysis, analysis). I ...
''P''(''x'') dates from a time when the distinction between a polynomial and the associated function was unclear. Moreover, the functional notation is often useful for specifying, in a single phrase, a polynomial and its indeterminate. For example, "let ''P''(''x'') be a polynomial" is a shorthand for "let ''P'' be a polynomial in the indeterminate ''x''". On the other hand, when it is not necessary to emphasize the name of the indeterminate, many formulas are much simpler and easier to read if the name(s) of the indeterminate(s) do not appear at each occurrence of the polynomial. The ambiguity of having two notations for a single mathematical object may be formally resolved by considering the general meaning of the functional notation for polynomials. If ''a'' denotes a number, a variable, another polynomial, or, more generally, any expression, then ''P''(''a'') denotes, by convention, the result of substituting ''a'' for ''x'' in ''P''. Thus, the polynomial ''P'' defines the function :$a\mapsto P\left(a\right),$ which is the ''polynomial function'' associated to ''P''. Frequently, when using this notation, one supposes that ''a'' is a number. However, one may use it over any domain where addition and multiplication are defined (that is, any ring). In particular, if ''a'' is a polynomial then ''P''(''a'') is also a polynomial. More specifically, when ''a'' is the indeterminate ''x'', then the
image File:TEIDE.JPG, An Synthetic aperture radar, SAR radar imaging, radar image acquired by the SIR-C/X-SAR radar on board the Space Shuttle Endeavour shows the Teide volcano. The city of Santa Cruz de Tenerife is visible as the purple and white a ...
of ''x'' by this function is the polynomial ''P'' itself (substituting ''x'' for ''x'' does not change anything). In other words, :$P\left(x\right)=P,$ which justifies formally the existence of two notations for the same polynomial.

# Definition

A ''polynomial expression'' is an expression that can be built from constants and symbols called ''variables'' or ''indeterminates'' by means of
addition Addition (usually signified by the plus symbol ) is one of the four basic operations of arithmetic Arithmetic (from the Ancient Greek, Greek wikt:en:ἀριθμός#Ancient Greek, ἀριθμός ''arithmos'', 'number' and wikt:en:τική#An ...
,
multiplication Multiplication (often denoted by the cross symbol , by the mid-line dot operator , by juxtaposition, or, on computers, by an asterisk ) is one of the four elementary Operation (mathematics), mathematical operations of arithmetic, with the ...

and
exponentiation Exponentiation is a mathematical operation, written as , involving two numbers, the '' base'' and the ''exponent'' or ''power'' , and pronounced as " raised to the power of ". When is a positive integer An integer (from the Latin wikt: ...
to a
non-negative integer In mathematics Mathematics (from Ancient Greek, Greek: ) includes the study of such topics as quantity (number theory), mathematical structure, structure (algebra), space (geometry), and calculus, change (mathematical analysis, analysis). ...
power. The constants are generally
number A number is a mathematical object A mathematical object is an abstract concept arising in mathematics. In the usual language of mathematics, an ''object'' is anything that has been (or could be) formally defined, and with which one may do deduct ...

s, but may be any expression that do not involve the indeterminates, and represent
mathematical object A mathematical object is an abstract concept arising in mathematics. In the usual language of mathematics, an ''object'' is anything that has been (or could be) formally defined, and with which one may do deductive reasoning and mathematical proofs ...
s that can be added and multiplied. Two polynomial expressions are considered as defining the same ''polynomial'' if they may be transformed, one to the other, by applying the usual properties of
commutativity In mathematics Mathematics (from Ancient Greek, Greek: ) includes the study of such topics as quantity (number theory), mathematical structure, structure (algebra), space (geometry), and calculus, change (mathematical analysis, analysis). I ...
,
associativity In mathematics, the associative property is a property of some binary operations, which means that rearranging the parentheses in an expression will not change the result. In propositional logic, associativity is a Validity (logic), valid rule ...
and
distributivity In mathematics Mathematics (from Ancient Greek, Greek: ) includes the study of such topics as quantity (number theory), mathematical structure, structure (algebra), space (geometry), and calculus, change (mathematical analysis, analysis). It ...
of addition and multiplication. For example $\left(x-1\right)\left(x-2\right)$ and $x^2-3x+2$ are two polynomial expressions that represent the same polynomial; so, one writes $\left(x-1\right)\left(x-2\right)=x^2-3x+2.$ A polynomial in a single indeterminate can always be written (or rewritten) in the form :$a_n x^n + a_x^ + \dotsb + a_2 x^2 + a_1 x + a_0,$ where $a_0, \ldots, a_n$ are constants that are called the ''coefficients'' of the polynomial, and $x$ is the indeterminate. The word "indeterminate" means that $x$ represents no particular value, although any value may be substituted for it. The mapping that associates the result of this substitution to the substituted value is a
function Function or functionality may refer to: Computing * Function key A function key is a key on a computer A computer is a machine that can be programmed to carry out sequences of arithmetic or logical operations automatically. Modern comp ...
, called a ''polynomial function''. This can be expressed more concisely by using summation notation: :$\sum_^n a_k x^k$ That is, a polynomial can either be zero or can be written as the sum of a finite number of non-zero terms. Each term consists of the product of a number called the
coefficient In mathematics, a coefficient is a multiplicative factor in some Summand, term of a polynomial, a series (mathematics), series, or any expression (mathematics), expression; it is usually a number, but may be any expression (including variables suc ...
of the term and a finite number of indeterminates, raised to nonnegative integer powers.

# Classification

The exponent on an indeterminate in a term is called the degree of that indeterminate in that term; the degree of the term is the sum of the degrees of the indeterminates in that term, and the degree of a polynomial is the largest degree of any term with nonzero coefficient. Because , the degree of an indeterminate without a written exponent is one. A term with no indeterminates and a polynomial with no indeterminates are called, respectively, a
constant term In mathematics Mathematics (from Ancient Greek, Greek: ) includes the study of such topics as quantity (number theory), mathematical structure, structure (algebra), space (geometry), and calculus, change (mathematical analysis, analysis). It h ...
and a constant polynomial. The degree of a constant term and of a nonzero constant polynomial is 0. The degree of the zero polynomial 0 (which has no terms at all) is generally treated as not defined (but see below). For example: :$-5x^2y$ is a term. The coefficient is , the indeterminates are and , the degree of is two, while the degree of is one. The degree of the entire term is the sum of the degrees of each indeterminate in it, so in this example the degree is . Forming a sum of several terms produces a polynomial. For example, the following is a polynomial: :$\underbrace_ \underbrace_ \underbrace_.$ It consists of three terms: the first is degree two, the second is degree one, and the third is degree zero. Polynomials of small degree have been given specific names. A polynomial of degree zero is a ''constant polynomial'', or simply a ''constant''. Polynomials of degree one, two or three are respectively ''linear polynomials,'' ''
quadratic polynomial In algebra, a quadratic function, a quadratic polynomial, a polynomial of degree 2, or simply a quadratic, is a polynomial function with one or more variables in which the highest-degree term is of the second degree. root of a polynomial, roots (c ...
s'' and ''cubic polynomials''. For higher degrees, the specific names are not commonly used, although ''quartic polynomial'' (for degree four) and ''quintic polynomial'' (for degree five) are sometimes used. The names for the degrees may be applied to the polynomial or to its terms. For example, the term in is a linear term in a quadratic polynomial. The polynomial 0, which may be considered to have no terms at all, is called the zero polynomial. Unlike other constant polynomials, its degree is not zero. Rather, the degree of the zero polynomial is either left explicitly undefined, or defined as negative (either −1 or −∞). The zero polynomial is also unique in that it is the only polynomial in one indeterminate that has an infinite number of
roots A root is the part of a plant that most often lies below the surface of the soil but can also be aerial or aerating, that is, growing up above the ground or especially above water. Root or roots may also refer to: Art, entertainment, and media * ...
. The graph of the zero polynomial, , is the ''x''-axis. In the case of polynomials in more than one indeterminate, a polynomial is called ''homogeneous'' of if ''all'' of its non-zero terms have . The zero polynomial is homogeneous, and, as a homogeneous polynomial, its degree is undefined. For example, is homogeneous of degree 5. For more details, see
Homogeneous polynomial In mathematics Mathematics (from Ancient Greek, Greek: ) includes the study of such topics as quantity (number theory), mathematical structure, structure (algebra), space (geometry), and calculus, change (mathematical analysis, analysis). I ...
. The
commutative law In mathematics Mathematics (from Ancient Greek, Greek: ) includes the study of such topics as quantity (number theory), mathematical structure, structure (algebra), space (geometry), and calculus, change (mathematical analysis, analysis). I ...
of addition can be used to rearrange terms into any preferred order. In polynomials with one indeterminate, the terms are usually ordered according to degree, either in "descending powers of ", with the term of largest degree first, or in "ascending powers of ". The polynomial is written in descending powers of . The first term has coefficient , indeterminate , and exponent . In the second term, the coefficient . The third term is a constant. Because the ''degree'' of a non-zero polynomial is the largest degree of any one term, this polynomial has degree two. Two terms with the same indeterminates raised to the same powers are called "similar terms" or "like terms", and they can be combined, using the
distributive law In mathematics Mathematics (from Ancient Greek, Greek: ) includes the study of such topics as quantity (number theory), mathematical structure, structure (algebra), space (geometry), and calculus, change (mathematical analysis, analysis). It ...
, into a single term whose coefficient is the sum of the coefficients of the terms that were combined. It may happen that this makes the coefficient 0. Polynomials can be classified by the number of terms with nonzero coefficients, so that a one-term polynomial is called a
monomial In mathematics, a monomial is, roughly speaking, a polynomial which has only one summand, term. Two definitions of a monomial may be encountered: # A monomial, also called power product, is a product of powers of Variable (mathematics), variables wi ...
, a two-term polynomial is called a binomial, and a three-term polynomial is called a ''trinomial''. The term "quadrinomial" is occasionally used for a four-term polynomial. A real polynomial is a polynomial with
real Real may refer to: * Reality Reality is the sum or aggregate of all that is real or existent within a system, as opposed to that which is only Object of the mind, imaginary. The term is also used to refer to the ontological status of things, ind ...
coefficients. When it is used to define a
function Function or functionality may refer to: Computing * Function key A function key is a key on a computer A computer is a machine that can be programmed to carry out sequences of arithmetic or logical operations automatically. Modern comp ...
, the
domain Domain may refer to: Mathematics *Domain of a function, the set of input values for which the (total) function is defined **Domain of definition of a partial function **Natural domain of a partial function **Domain of holomorphy of a function *Doma ...
is not so restricted. However, a real polynomial function is a function from the reals to the reals that is defined by a real polynomial. Similarly, an integer polynomial is a polynomial with
integer An integer (from the Latin Latin (, or , ) is a classical language belonging to the Italic languages, Italic branch of the Indo-European languages. Latin was originally spoken in the area around Rome, known as Latium. Through the power of t ...
coefficients, and a complex polynomial is a polynomial with
complex The UCL Faculty of Mathematical and Physical Sciences is one of the 11 constituent faculties of University College London , mottoeng = Let all come who by merit deserve the most reward , established = , type = Public university, Public rese ...
coefficients. A polynomial in one indeterminate is called a ''
univariateIn mathematics, a univariate object is an expression, equation In mathematics, an equation is a statement that asserts the equality (mathematics), equality of two Expression (mathematics), expressions, which are connected by the equals sign "=". ...
polynomial'', a polynomial in more than one indeterminate is called a multivariate polynomial. A polynomial with two indeterminates is called a bivariate polynomial. These notions refer more to the kind of polynomials one is generally working with than to individual polynomials; for instance, when working with univariate polynomials, one does not exclude constant polynomials (which may result from the subtraction of non-constant polynomials), although strictly speaking, constant polynomials do not contain any indeterminates at all. It is possible to further classify multivariate polynomials as ''bivariate'', ''trivariate'', and so on, according to the maximum number of indeterminates allowed. Again, so that the set of objects under consideration be closed under subtraction, a study of trivariate polynomials usually allows bivariate polynomials, and so on. It is also common to say simply "polynomials in , and ", listing the indeterminates allowed. The evaluation of a polynomial consists of substituting a numerical value to each indeterminate and carrying out the indicated multiplications and additions. For polynomials in one indeterminate, the evaluation is usually more efficient (lower number of arithmetic operations to perform) using Horner's method: :$\left(\left(\left(\left(\left(a_n x + a_\right)x + a_\right)x + \dotsb + a_3\right)x + a_2\right)x + a_1\right)x + a_0.$

# Arithmetic

Polynomials can be added using the
associative law In mathematics Mathematics (from Ancient Greek, Greek: ) includes the study of such topics as quantity (number theory), mathematical structure, structure (algebra), space (geometry), and calculus, change (mathematical analysis, analysis). ...
of addition (grouping all their terms together into a single sum), possibly followed by reordering (using the
commutative law In mathematics Mathematics (from Ancient Greek, Greek: ) includes the study of such topics as quantity (number theory), mathematical structure, structure (algebra), space (geometry), and calculus, change (mathematical analysis, analysis). I ...
) and combining of like terms. For example, if :$P = 3x^2 - 2x + 5xy - 2$ and $Q = -3x^2 + 3x + 4y^2 + 8$ then the sum :$P + Q = 3x^2 - 2x + 5xy - 2 - 3x^2 + 3x + 4y^2 + 8$ can be reordered and regrouped as :$P + Q = \left(3x^2 - 3x^2\right) + \left(- 2x + 3x\right) + 5xy + 4y^2 + \left(8 - 2\right)$ and then simplified to :$P + Q = x + 5xy + 4y^2 + 6.$ When polynomials are added together, the result is another polynomial. Subtraction of polynomials is similar.

## Multiplication

Polynomials can also be multiplied. To expand the product of two polynomials into a sum of terms, the distributive law is repeatedly applied, which results in each term of one polynomial being multiplied by every term of the other. For example, if :$\begin \color P &\color \\ \color Q &\color \end$ then :$\begin & &&\left(\cdot\right) &+&\left(\cdot\right)&+&\left(\cdot \right)&+&\left(\cdot\right) \\&&+&\left(\cdot\right)&+&\left(\cdot\right)&+&\left(\cdot \right)&+& \left(\cdot\right) \\&&+&\left(\cdot\right)&+&\left(\cdot\right)&+& \left(\cdot \right)&+&\left(\cdot\right) \end$ Carrying out the multiplication in each term produces :$\begin PQ & = && 4x^2 &+& 10xy &+& 2x^2y &+& 2x \\ &&+& 6xy &+& 15y^2 &+& 3xy^2 &+& 3y \\ &&+& 10x &+& 25y &+& 5xy &+& 5. \end$ Combining similar terms yields :$\begin PQ & = && 4x^2 &+&\left( 10xy + 6xy + 5xy \right) &+& 2x^2y &+& \left( 2x + 10x \right) \\ && + & 15y^2 &+& 3xy^2 &+&\left( 3y + 25y \right)&+&5 \end$ which can be simplified to :$PQ = 4x^2 + 21xy + 2x^2y + 12x + 15y^2 + 3xy^2 + 28y + 5.$ As in the example, the product of polynomials is always a polynomial.

## Composition

Given a polynomial $f$ of a single variable and another polynomial of any number of variables, the
composition Composition or Compositions may refer to: Arts * Composition (dance), practice and teaching of choreography * Composition (music), an original piece of music and its creation *Composition (visual arts) The term composition means "putting togethe ...
$f \circ g$ is obtained by substituting each copy of the variable of the first polynomial by the second polynomial. For example, if $f\left(x\right) = x^2 + 2x$ and $g\left(x\right) = 3x + 2$ then $(f\circ g)(x) = f(g(x)) = (3x + 2)^2 + 2(3x + 2).$ A composition may be expanded to a sum of terms using the rules for multiplication and division of polynomials. The composition of two polynomials is another polynomial.

## Division

The division of one polynomial by another is not typically a polynomial. Instead, such ratios are a more general family of objects, called ''
rational fraction In algebra Algebra (from ar, الجبر, lit=reunion of broken parts, bonesetting, translit=al-jabr) is one of the areas of mathematics, broad areas of mathematics, together with number theory, geometry and mathematical analysis, analysis. In ...
s'', ''rational expressions'', or ''
rational function In mathematics Mathematics (from Ancient Greek, Greek: ) includes the study of such topics as quantity (number theory), mathematical structure, structure (algebra), space (geometry), and calculus, change (mathematical analysis, analysis). I ...

s'', depending on context. This is analogous to the fact that the ratio of two
integer An integer (from the Latin Latin (, or , ) is a classical language belonging to the Italic languages, Italic branch of the Indo-European languages. Latin was originally spoken in the area around Rome, known as Latium. Through the power of t ...
s is a
rational number In mathematics Mathematics (from Ancient Greek, Greek: ) includes the study of such topics as quantity (number theory), mathematical structure, structure (algebra), space (geometry), and calculus, change (mathematical analysis, analysis). ...
, not necessarily an integer. For example, the fraction is not a polynomial, and it cannot be written as a finite sum of powers of the variable . For polynomials in one variable, there is a notion of
Euclidean division of polynomials In algebra, the greatest common divisor (frequently abbreviated as GCD) of two polynomials is a polynomial, of the highest possible degree, that is a factor of both the two original polynomials. This concept is analogous to the greatest common ...
, generalizing the
Euclidean division In arithmetic, Euclidean division – or division with remainder – is the process of division (mathematics), dividing one integer (the dividend) by another (the divisor), in a way that produces a quotient and a remainder smaller than the divisor ...
of integers. This notion of the division results in two polynomials, a ''quotient'' and a ''remainder'' , such that and . The quotient and remainder may be computed by any of several algorithms, including
polynomial long division In algebra Algebra (from ar, الجبر, lit=reunion of broken parts, bonesetting, translit=al-jabr) is one of the areas of mathematics, broad areas of mathematics, together with number theory, geometry and mathematical analysis, analysis. In ...
and
synthetic division In algebra Algebra (from ar, الجبر, lit=reunion of broken parts, bonesetting, translit=al-jabr) is one of the areas of mathematics, broad areas of mathematics, together with number theory, geometry and mathematical analysis, analysis. In ...
. When the denominator is monic and linear, that is, for some constant , then the
polynomial remainder theorem In algebra, the polynomial remainder theorem or little Bézout's theorem (named after Étienne Bézout) is an application of Euclidean division of polynomials. It states that the remainder of the division of a polynomial f(x) by a linear polynomia ...
asserts that the remainder of the division of by is the
evaluation Evaluation is a system A system is a group of Interaction, interacting or interrelated elements that act according to a set of rules to form a unified whole. A system, surrounded and influenced by its environment, is described by its boundarie ...
. In this case, the quotient may be computed by
Ruffini's rule In mathematics Mathematics (from Ancient Greek, Greek: ) includes the study of such topics as quantity (number theory), mathematical structure, structure (algebra), space (geometry), and calculus, change (mathematical analysis, analysis). It h ...
, a special case of synthetic division.

## Factoring

All polynomials with coefficients in a
unique factorization domain In mathematics Mathematics (from Ancient Greek, Greek: ) includes the study of such topics as quantity (number theory), mathematical structure, structure (algebra), space (geometry), and calculus, change (mathematical analysis, analysis). It ...
(for example, the integers or a
field Field may refer to: Expanses of open ground * Field (agriculture), an area of land used for agricultural purposes * Airfield, an aerodrome that lacks the infrastructure of an airport * Battlefield * Lawn, an area of mowed grass * Meadow, a grassl ...
) also have a factored form in which the polynomial is written as a product of
irreducible polynomial In mathematics Mathematics (from Ancient Greek, Greek: ) includes the study of such topics as quantity (number theory), mathematical structure, structure (algebra), space (geometry), and calculus, change (mathematical analysis, analysis). It ...
s and a constant. This factored form is unique up to the order of the factors and their multiplication by an invertible constant. In the case of the field of
complex number In mathematics Mathematics (from Ancient Greek, Greek: ) includes the study of such topics as quantity (number theory), mathematical structure, structure (algebra), space (geometry), and calculus, change (mathematical analysis, analysis). I ...

s, the irreducible factors are linear. Over the
real number In mathematics Mathematics (from Ancient Greek, Greek: ) includes the study of such topics as quantity (number theory), mathematical structure, structure (algebra), space (geometry), and calculus, change (mathematical analysis, analysis). ...
s, they have the degree either one or two. Over the integers and the
rational number In mathematics Mathematics (from Ancient Greek, Greek: ) includes the study of such topics as quantity (number theory), mathematical structure, structure (algebra), space (geometry), and calculus, change (mathematical analysis, analysis). ...
s the irreducible factors may have any degree. For example, the factored form of :$5x^3-5$ is :$5\left(x - 1\right)\left\left(x^2 + x + 1\right\right)$ over the integers and the reals, and :$5\left(x - 1\right)\left\left(x + \frac\right\right)\left\left(x + \frac\right\right)$ over the complex numbers. The computation of the factored form, called ''factorization'' is, in general, too difficult to be done by hand-written computation. However, efficient
polynomial factorization In mathematics Mathematics (from Ancient Greek, Greek: ) includes the study of such topics as quantity (number theory), mathematical structure, structure (algebra), space (geometry), and calculus, change (mathematical analysis, analysis). I ...
algorithm of an algorithm (Euclid's algorithm) for calculating the greatest common divisor (g.c.d.) of two numbers ''a'' and ''b'' in locations named A and B. The algorithm proceeds by successive subtractions in two loops: IF the test B ≥ A yields "yes" ...

s are available in most
computer algebra system A computer algebra system (CAS) or symbolic algebra system (SAS) is any mathematical software with the ability to manipulate mathematical expressions in a way similar to the traditional manual computations of mathematicians and scientists. The deve ...

s.

## Calculus

Calculating
derivative In mathematics, the derivative of a function of a real variable measures the sensitivity to change of the function value (output value) with respect to a change in its Argument of a function, argument (input value). Derivatives are a fundament ...

s and integrals of polynomials is particularly simple, compared to other kinds of functions. The
derivative In mathematics, the derivative of a function of a real variable measures the sensitivity to change of the function value (output value) with respect to a change in its Argument of a function, argument (input value). Derivatives are a fundament ...

of the polynomial $P = a_n x^n + a_ x^ + \dots + a_2 x^2 + a_1 x + a_0 = \sum_^n a_i x^i$ with respect to is the polynomial $n a_n x^ + (n - 1)a_ x^ + \dots + 2 a_2 x + a_1 = \sum_^n i a_i x^.$ Similarly, the general
antiderivative In calculus Calculus, originally called infinitesimal calculus or "the calculus of infinitesimal In mathematics, infinitesimals or infinitesimal numbers are quantities that are closer to zero than any standard real number, but are not zer ...
(or indefinite integral) of $P$ is $\frac + \frac + \dots + \frac + \frac + a_0 x + c = c + \sum_^n \frac$ where is an arbitrary constant. For example, antiderivatives of have the form . For polynomials whose coefficients come from more abstract settings (for example, if the coefficients are integers modulo some
prime number A prime number (or a prime) is a natural number greater than 1 that is not a Product (mathematics), product of two smaller natural numbers. A natural number greater than 1 that is not prime is called a composite number. For example, 5 is prime ...
, or elements of an arbitrary ring), the formula for the derivative can still be interpreted formally, with the coefficient understood to mean the sum of copies of . For example, over the integers modulo , the derivative of the polynomial is the polynomial .

# Polynomial functions

A ''polynomial function'' is a function that can be defined by evaluating a polynomial. More precisely, a function of one
argument In logic Logic is an interdisciplinary field which studies truth and reasoning Reason is the capacity of consciously making sense of things, applying logic Logic (from Ancient Greek, Greek: grc, wikt:λογική, λογική, lab ...
from a given domain is a polynomial function if there exists a polynomial :$a_n x^n + a_ x^ + \cdots + a_2 x^2 + a_1 x + a_0$ that evaluates to $f\left(x\right)$ for all in the
domain Domain may refer to: Mathematics *Domain of a function, the set of input values for which the (total) function is defined **Domain of definition of a partial function **Natural domain of a partial function **Domain of holomorphy of a function *Doma ...
of (here, is a non-negative integer and are constant coefficients). Generally, unless otherwise specified, polynomial functions have
complex The UCL Faculty of Mathematical and Physical Sciences is one of the 11 constituent faculties of University College London , mottoeng = Let all come who by merit deserve the most reward , established = , type = Public university, Public rese ...
coefficients, arguments, and values. In particular, a polynomial, restricted to have real coefficients, defines a function from the complex numbers to the complex numbers. If the domain of this function is also restricted to the reals, the resulting function is a
real function In mathematical analysis, and applications in geometry Geometry (from the grc, γεωμετρία; ''wikt:γῆ, geo-'' "earth", ''wikt:μέτρον, -metron'' "measurement") is, with arithmetic, one of the oldest branches of mathematics. ...
that maps reals to reals. For example, the function , defined by :$f\left(x\right) = x^3 - x,$ is a polynomial function of one variable. Polynomial functions of several variables are similarly defined, using polynomials in more than one indeterminate, as in :$f\left(x,y\right)= 2x^3+4x^2y+xy^5+y^2-7.$ According to the definition of polynomial functions, there may be expressions that obviously are not polynomials but nevertheless define polynomial functions. An example is the expression $\left\left(\sqrt\right\right)^2,$ which takes the same values as the polynomial $1-x^2$ on the interval
continuous Continuity or continuous may refer to: Mathematics * Continuity (mathematics), the opposing concept to discreteness; common examples include ** Continuous probability distribution or random variable in probability and statistics ** Continuous ga ...
,
smooth Smooth may refer to: Mathematics * Smooth function is a smooth function with compact support. In mathematical analysis, the smoothness of a function is a property measured by the number of continuous derivatives it has over some domain. ...

, and
entire *In philately, see Cover (philately), Cover *In mathematics, see Entire function *In animal fancy and animal husbandry, entire (animal), entire indicates that an animal has not been desexed, that is, spayed or neutered *In botany, an edge (such as o ...
.

## Graphs

File:Algebra1 fnz fig037 pc.svg, Polynomial of degree 0:
File:Fonction de Sophie Germain.png, Polynomial of degree 1:
File:Polynomialdeg2.svg, Polynomial of degree 2:

File:Polynomialdeg3.svg, Polynomial of degree 3:

File:Polynomialdeg4.svg, Polynomial of degree 4:
File:Quintic polynomial.svg, Polynomial of degree 5:
File:Sextic Graph.svg, Polynomial of degree 6:

File:Septic graph.svg, Polynomial of degree 7:

A polynomial function in one real variable can be represented by a
graph Graph may refer to: Mathematics *Graph (discrete mathematics), a structure made of vertices and edges **Graph theory, the study of such graphs and their properties *Graph (topology), a topological space resembling a graph in the sense of discret ...

.
• The graph of the zero polynomial is the -axis.
• The graph of a degree 0 polynomial is a horizontal line with
• The graph of a degree 1 polynomial (or linear function) is an oblique line with and
slope In mathematics, the slope or gradient of a line Line, lines, The Line, or LINE may refer to: Arts, entertainment, and media Films * ''Lines'' (film), a 2016 Greek film * ''The Line'' (2017 film) * ''The Line'' (2009 film) * ''The Line'', a ...

.
• The graph of a degree 2 polynomial is a
parabola The parabola is a member of the family of conic sections. In mathematics Mathematics (from Ancient Greek, Greek: ) includes the study of such topics as quantity (number theory), mathematical structure, structure (algebra), space (geometry ...

.
• The graph of a degree 3 polynomial is a
cubic curve In mathematics Mathematics (from Ancient Greek, Greek: ) includes the study of such topics as quantity (number theory), mathematical structure, structure (algebra), space (geometry), and calculus, change (mathematical analysis, analysis). It ...

.
• The graph of any polynomial with degree 2 or greater is a continuous non-linear curve.
A non-constant polynomial function when the variable increases indefinitely (in
absolute value of the absolute value function for real numbers In mathematics Mathematics (from Ancient Greek, Greek: ) includes the study of such topics as quantity (number theory), mathematical structure, structure (algebra), space (geometry), and calc ...

). If the degree is higher than one, the graph does not have any
asymptote 250px, A curve intersecting an asymptote infinitely many times. In analytic geometry In classical mathematics, analytic geometry, also known as coordinate geometry or Cartesian geometry, is the study of geometry Geometry (from the grc ...

. It has two parabolic branches with vertical direction (one branch for positive ''x'' and one for negative ''x''). Polynomial graphs are analyzed in calculus using intercepts, slopes, concavity, and end behavior.

# Equations

A ''polynomial equation'', also called an ''
algebraic equation In mathematics Mathematics (from Ancient Greek, Greek: ) includes the study of such topics as quantity (number theory), mathematical structure, structure (algebra), space (geometry), and calculus, change (mathematical analysis, analysis). It h ...
'', is an
equation In mathematics Mathematics (from Ancient Greek, Greek: ) includes the study of such topics as quantity (number theory), mathematical structure, structure (algebra), space (geometry), and calculus, change (mathematical analysis, analysis). I ...

of the form :$a_n x^n + a_x^ + \dotsb + a_2 x^2 + a_1 x + a_0 = 0.$ For example, :$3x^2 + 4x -5 = 0$ is a polynomial equation. When considering equations, the indeterminates (variables) of polynomials are also called
unknown Unknown or The Unknown may refer to: Film * The Unknown (1915 comedy film), ''The Unknown'' (1915 comedy film), a silent boxing film * The Unknown (1915 drama film), ''The Unknown'' (1915 drama film) * The Unknown (1927 film), ''The Unknown'' (19 ...
s, and the ''solutions'' are the possible values of the unknowns for which the equality is true (in general more than one solution may exist). A polynomial equation stands in contrast to a ''polynomial
identity Identity may refer to: Social sciences * Identity (social science), personhood or group affiliation in psychology and sociology Group expression and affiliation * Cultural identity, a person's self-affiliation (or categorization by others ...
'' like , where both expressions represent the same polynomial in different forms, and as a consequence any evaluation of both members gives a valid equality. In elementary
algebra Algebra (from ar, الجبر, lit=reunion of broken parts, bonesetting, translit=al-jabr) is one of the areas of mathematics, broad areas of mathematics, together with number theory, geometry and mathematical analysis, analysis. In its most ge ...
, methods such as the
quadratic formula In elementary algebra Elementary algebra encompasses some of the basic concepts of algebra, one of the main branches of mathematics. It is typically taught to secondary school students and builds on their understanding of arithmetic. Whereas ar ...

are taught for solving all first degree and second degree polynomial equations in one variable. There are also formulas for the
cubic Cubic may refer to: Science and mathematics * Cube (algebra), "cubic" measurement * Cube, a three-dimensional solid object bounded by six square faces, facets or sides, with three meeting at each vertex ** Cubic crystal system 200px, A network ...

and
quartic equation In mathematics Mathematics (from Ancient Greek, Greek: ) includes the study of such topics as quantity (number theory), mathematical structure, structure (algebra), space (geometry), and calculus, change (mathematical analysis, analysis). It h ...
s. For higher degrees, the
Abel–Ruffini theorem In mathematics, the Abel–Ruffini theorem (also known as Abel's impossibility theorem) states that there is no solution in radicals to general algebraic equation, polynomial equations of quintic equation, degree five or higher with arbitrary coef ...
asserts that there can not exist a general formula in radicals. However,
root-finding algorithm In mathematics and computing, a root-finding algorithm is an algorithm for finding Zero of a function, zeroes, also called "roots", of continuous functions. A zero of a function , from the real numbers to real numbers or from the complex numbers to ...
s may be used to find
numerical approximation (c. 1800–1600 BC) with annotations. The approximation of the square root of 2 is four sexagesimal figures, which is about six decimal figures. 1 + 24/60 + 51/602 + 10/603 = 1.41421296... Numerical analysis is the study of algorithms that use num ...
s of the roots of a polynomial expression of any degree. The number of solutions of a polynomial equation with real coefficients may not exceed the degree, and equals the degree when the
complex The UCL Faculty of Mathematical and Physical Sciences is one of the 11 constituent faculties of University College London , mottoeng = Let all come who by merit deserve the most reward , established = , type = Public university, Public rese ...
solutions are counted with their multiplicity. This fact is called the
fundamental theorem of algebra The fundamental theorem of algebra states that every non- constant single-variable polynomial In mathematics Mathematics (from Ancient Greek, Greek: ) includes the study of such topics as quantity (number theory), mathematical structure, s ...
.

## Solving equations

A ''root'' of a nonzero univariate polynomial is a value of such that . In other words, a root of is a solutions of the
polynomial equation In mathematics Mathematics (from Ancient Greek, Greek: ) includes the study of such topics as quantity (number theory), mathematical structure, structure (algebra), space (geometry), and calculus, change (mathematical analysis, analysis). It h ...
or a
zero 0 (zero) is a number A number is a mathematical object used to counting, count, measurement, measure, and nominal number, label. The original examples are the natural numbers 1, 2, 3, 4, and so forth. Numbers can be represented in languag ...
of the polynomial function defined by . In the case of the zero polynomial, every number is ia zero of the corresponding function, and the concept of root is rarely cosidered. A number is a root of a polynomial if and only if the
linear polynomial In mathematics Mathematics (from Ancient Greek, Greek: ) includes the study of such topics as quantity (number theory), mathematical structure, structure (algebra), space (geometry), and calculus, change (mathematical analysis, analysis). I ...
divides , that is if there is another polynomial such that . It may happen that a power (greater than ) of divides ; in this case, is a ''multiple root'' of , and otherwise is simple root of . If is a nonzero polynomial, there is a highest power such that divides , which is called the ''multiplicity'' of as a root of . The number of roots of a nonzero polynomial , counted with their respective multiplicities, cannot exceed the degree of , and equals this degree if all
complex The UCL Faculty of Mathematical and Physical Sciences is one of the 11 constituent faculties of University College London , mottoeng = Let all come who by merit deserve the most reward , established = , type = Public university, Public rese ...
roots are considered (this is a consequence of the
fundamental theorem of algebra The fundamental theorem of algebra states that every non- constant single-variable polynomial In mathematics Mathematics (from Ancient Greek, Greek: ) includes the study of such topics as quantity (number theory), mathematical structure, s ...
. The the coefficients of a polynomial and its roots are related by Vieta's formulas. Some polynomials, such as , do not have any roots among the
real number In mathematics Mathematics (from Ancient Greek, Greek: ) includes the study of such topics as quantity (number theory), mathematical structure, structure (algebra), space (geometry), and calculus, change (mathematical analysis, analysis). ...
s. If, however, the set of accepted solutions is expanded to the
complex number In mathematics Mathematics (from Ancient Greek, Greek: ) includes the study of such topics as quantity (number theory), mathematical structure, structure (algebra), space (geometry), and calculus, change (mathematical analysis, analysis). I ...

s, every non-constant polynomial has at least one root; this is the
fundamental theorem of algebra The fundamental theorem of algebra states that every non- constant single-variable polynomial In mathematics Mathematics (from Ancient Greek, Greek: ) includes the study of such topics as quantity (number theory), mathematical structure, s ...
. By successively dividing out factors , one sees that any polynomial with complex coefficients can be written as a constant (its leading coefficient) times a product of such polynomial factors of degree 1; as a consequence, the number of (complex) roots counted with their multiplicities is exactly equal to the degree of the polynomial. There may be several meanings of "solving an equation". One may want to express the solutions as explicit numbers; for example, the unique solution of is . Unfortunately, this is, in general, impossible for equations of degree greater than one, and, since the ancient times, mathematicians have searched to express the solutions as algebraic expression; for example the golden ratio $\left(1+\sqrt 5\right)/2$ is the unique positive solution of $x^2-x-1=0.$ In the ancient times, they succeeded only for degrees one and two. For quadratic equations, the
quadratic formula In elementary algebra Elementary algebra encompasses some of the basic concepts of algebra, one of the main branches of mathematics. It is typically taught to secondary school students and builds on their understanding of arithmetic. Whereas ar ...

provides such expressions of the solutions. Since the 16th century, similar formulas (using cube roots in addition to square roots), but much more complicated are known for equations of degree three and four (see cubic equation and
quartic equation In mathematics Mathematics (from Ancient Greek, Greek: ) includes the study of such topics as quantity (number theory), mathematical structure, structure (algebra), space (geometry), and calculus, change (mathematical analysis, analysis). It h ...
). But formulas for degree 5 and higher eluded researchers for several centuries. In 1824, Niels Henrik Abel proved the striking result that there are equations of degree 5 whose solutions cannot be expressed by a (finite) formula, involving only arithmetic operations and radicals (see
Abel–Ruffini theorem In mathematics, the Abel–Ruffini theorem (also known as Abel's impossibility theorem) states that there is no solution in radicals to general algebraic equation, polynomial equations of quintic equation, degree five or higher with arbitrary coef ...
). In 1830, Évariste Galois proved that most equations of degree higher than four cannot be solved by radicals, and showed that for each equation, one may decide whether it is solvable by radicals, and, if it is, solve it. This result marked the start of Galois theory and group theory, two important branches of modern
algebra Algebra (from ar, الجبر, lit=reunion of broken parts, bonesetting, translit=al-jabr) is one of the areas of mathematics, broad areas of mathematics, together with number theory, geometry and mathematical analysis, analysis. In its most ge ...
. Galois himself noted that the computations implied by his method were impracticable. Nevertheless, formulas for solvable equations of degrees 5 and 6 have been published (see quintic function and sextic equation). When there is no algebraic expression for the roots, and when such an algebraic expression exists but is too complicated to be useful, the unique way of solving is to compute
numerical approximation (c. 1800–1600 BC) with annotations. The approximation of the square root of 2 is four sexagesimal figures, which is about six decimal figures. 1 + 24/60 + 51/602 + 10/603 = 1.41421296... Numerical analysis is the study of algorithms that use num ...
s of the solutions. There are many methods for that; some are restricted to polynomials and others may apply to any continuous function. The most efficient
algorithm of an algorithm (Euclid's algorithm) for calculating the greatest common divisor (g.c.d.) of two numbers ''a'' and ''b'' in locations named A and B. The algorithm proceeds by successive subtractions in two loops: IF the test B ≥ A yields "yes" ...

s allow solving easily (on a computer) polynomial equations of degree higher than 1,000 (see Root-finding algorithm). For polynomials in more than one indeterminate, the combinations of values for the variables for which the polynomial function takes the value zero are generally called ''zeros'' instead of "roots". The study of the sets of zeros of polynomials is the object of
algebraic geometry Algebraic geometry is a branch of mathematics Mathematics (from Ancient Greek, Greek: ) includes the study of such topics as quantity (number theory), mathematical structure, structure (algebra), space (geometry), and calculus, change (ma ...
. For a set of polynomial equations in several unknowns, there are
algorithm of an algorithm (Euclid's algorithm) for calculating the greatest common divisor (g.c.d.) of two numbers ''a'' and ''b'' in locations named A and B. The algorithm proceeds by successive subtractions in two loops: IF the test B ≥ A yields "yes" ...

s to decide whether they have a finite number of
complex The UCL Faculty of Mathematical and Physical Sciences is one of the 11 constituent faculties of University College London , mottoeng = Let all come who by merit deserve the most reward , established = , type = Public university, Public rese ...
solutions, and, if this number is finite, for computing the solutions. See System of polynomial equations. The special case where all the polynomials are of degree one is called a system of linear equations, for which another range of different system of linear equations#Solving a linear system, solution methods exist, including the classical Gaussian elimination. A polynomial equation for which one is interested only in the solutions which are
integer An integer (from the Latin Latin (, or , ) is a classical language belonging to the Italic languages, Italic branch of the Indo-European languages. Latin was originally spoken in the area around Rome, known as Latium. Through the power of t ...
s is called a Diophantine equation. Solving Diophantine equations is generally a very hard task. It has been proved that there cannot be any general
algorithm of an algorithm (Euclid's algorithm) for calculating the greatest common divisor (g.c.d.) of two numbers ''a'' and ''b'' in locations named A and B. The algorithm proceeds by successive subtractions in two loops: IF the test B ≥ A yields "yes" ...

for solving them, and even for deciding whether the set of solutions is empty (see Hilbert's tenth problem). Some of the most famous problems that have been solved during the fifty last years are related to Diophantine equations, such as Fermat's Last Theorem.

# Generalizations

There are several generalizations of the concept of polynomials.

## Trigonometric polynomials

A trigonometric polynomial is a finite linear combination of function (mathematics), functions sin(''nx'') and cos(''nx'') with ''n'' taking on the values of one or more natural numbers. The coefficients may be taken as real numbers, for real-valued functions. If sin(''nx'') and cos(''nx'') are expanded in terms of sin(''x'') and cos(''x''), a trigonometric polynomial becomes a polynomial in the two variables sin(''x'') and cos(''x'') (using List of trigonometric identities#Multiple-angle formulae). Conversely, every polynomial in sin(''x'') and cos(''x'') may be converted, with List of trigonometric identities#Product-to-sum and sum-to-product identities, Product-to-sum identities, into a linear combination of functions sin(''nx'') and cos(''nx''). This equivalence explains why linear combinations are called polynomials. For complex number, complex coefficients, there is no difference between such a function and a finite Fourier series. Trigonometric polynomials are widely used, for example in trigonometric interpolation applied to the interpolation of periodic functions. They are used also in the discrete Fourier transform.

## Matrix polynomials

A matrix polynomial is a polynomial with square matrix, square matrices as variables. Given an ordinary, scalar-valued polynomial :$P\left(x\right) = \sum_^n =a_0 + a_1 x+ a_2 x^2 + \cdots + a_n x^n,$ this polynomial evaluated at a matrix ''A'' is :$P\left(A\right) = \sum_^n =a_0 I + a_1 A + a_2 A^2 + \cdots + a_n A^n,$ where ''I'' is the identity matrix. A matrix polynomial equation is an equality between two matrix polynomials, which holds for the specific matrices in question. A matrix polynomial identity is a matrix polynomial equation which holds for all matrices ''A'' in a specified matrix ring ''Mn''(''R'').

## Laurent polynomials

Laurent polynomials are like polynomials, but allow negative powers of the variable(s) to occur.

## Rational functions

A
rational fraction In algebra Algebra (from ar, الجبر, lit=reunion of broken parts, bonesetting, translit=al-jabr) is one of the areas of mathematics, broad areas of mathematics, together with number theory, geometry and mathematical analysis, analysis. In ...
is the quotient (algebraic fraction) of two polynomials. Any algebraic expression that can be rewritten as a rational fraction is a
rational function In mathematics Mathematics (from Ancient Greek, Greek: ) includes the study of such topics as quantity (number theory), mathematical structure, structure (algebra), space (geometry), and calculus, change (mathematical analysis, analysis). I ...

. While polynomial functions are defined for all values of the variables, a rational function is defined only for the values of the variables for which the denominator is not zero. The rational fractions include the Laurent polynomials, but do not limit denominators to powers of an indeterminate.

## Power series

Formal power series are like polynomials, but allow infinitely many non-zero terms to occur, so that they do not have finite degree. Unlike polynomials they cannot in general be explicitly and fully written down (just like irrational numbers cannot), but the rules for manipulating their terms are the same as for polynomials. Non-formal power series also generalize polynomials, but the multiplication of two power series may not converge.

## Other examples

A bivariate polynomial where the second variable is substituted by an exponential function applied to the first variable, for example , may be called an exponential polynomial.

# Polynomial ring

A ''polynomial'' over a commutative ring is a polynomial whose all coefficients belong to . It is straightforward to verify that the polynomials in a given set of indeterminates over form a commutative ring, called the ''polynomial ring'' in these indeterminates, denoted $R\left[x\right]$ in the univariate case and $R\left[x_1,\ldots, x_n\right]$ in the multivariate case. One has :$R\left[x_1,\ldots, x_n\right]=\left\left(R\left[x_1,\ldots, x_\right]\right\right)\left[x_n\right].$ So, most of the theory of the multivariate case can be reduced to an iterated univariate case. The map from to sending to itself considered as a constant polynomial is an injective ring homomorphism, by which is viewed as a subring of . In particular, is an algebra (ring theory), algebra over . One can think of the ring as arising from by adding one new element ''x'' to ''R'', and extending in a minimal way to a ring in which satisfies no other relations than the obligatory ones, plus commutation with all elements of (that is ). To do this, one must add all powers of and their linear combinations as well. Formation of the polynomial ring, together with forming factor rings by factoring out ideal (ring theory), ideals, are important tools for constructing new rings out of known ones. For instance, the ring (in fact field) of complex numbers, which can be constructed from the polynomial ring over the real numbers by factoring out the ideal of multiples of the polynomial . Another example is the construction of finite fields, which proceeds similarly, starting out with the field of integers modulo some
prime number A prime number (or a prime) is a natural number greater than 1 that is not a Product (mathematics), product of two smaller natural numbers. A natural number greater than 1 that is not prime is called a composite number. For example, 5 is prime ...
as the coefficient ring (see modular arithmetic). If is commutative, then one can associate with every polynomial in a ''polynomial function'' with domain and range equal to . (More generally, one can take domain and range to be any same unital algebra, unital associative algebra over .) One obtains the value by substitution (algebra), substitution of the value for the symbol in . One reason to distinguish between polynomials and polynomial functions is that, over some rings, different polynomials may give rise to the same polynomial function (see Fermat's little theorem for an example where is the integers modulo ). This is not the case when is the real or complex numbers, whence the two concepts are not always distinguished in analysis (mathematics), analysis. An even more important reason to distinguish between polynomials and polynomial functions is that many operations on polynomials (like
Euclidean division In arithmetic, Euclidean division – or division with remainder – is the process of division (mathematics), dividing one integer (the dividend) by another (the divisor), in a way that produces a quotient and a remainder smaller than the divisor ...
) require looking at what a polynomial is composed of as an expression rather than evaluating it at some constant value for .

## Divisibility

If is an integral domain and and are polynomials in , it is said that ''divides'' or is a divisor of if there exists a polynomial in such that . If $a\in R,$ then is a root of if and only $x-a$ divides . In this case, the quotient can be computed using the
polynomial long division In algebra Algebra (from ar, الجبر, lit=reunion of broken parts, bonesetting, translit=al-jabr) is one of the areas of mathematics, broad areas of mathematics, together with number theory, geometry and mathematical analysis, analysis. In ...
. If is a
field Field may refer to: Expanses of open ground * Field (agriculture), an area of land used for agricultural purposes * Airfield, an aerodrome that lacks the infrastructure of an airport * Battlefield * Lawn, an area of mowed grass * Meadow, a grassl ...
and and are polynomials in with , then there exist unique polynomials and in with :$f = q \, g + r$ and such that the degree of is smaller than the degree of (using the convention that the polynomial 0 has a negative degree). The polynomials and are uniquely determined by and . This is called ''Euclidean division of polynomials, Euclidean division, division with remainder'' or ''polynomial long division'' and shows that the ring is a Euclidean domain. Analogously, ''prime polynomials'' (more correctly, ''
irreducible polynomial In mathematics Mathematics (from Ancient Greek, Greek: ) includes the study of such topics as quantity (number theory), mathematical structure, structure (algebra), space (geometry), and calculus, change (mathematical analysis, analysis). It ...
s'') can be defined as ''non-zero polynomials which cannot be factorized into the product of two non-constant polynomials''. In the case of coefficients in a ring, ''"non-constant"'' must be replaced by ''"non-constant or non-unit (ring theory), unit"'' (both definitions agree in the case of coefficients in a field). Any polynomial may be decomposed into the product of an invertible constant by a product of irreducible polynomials. If the coefficients belong to a field or a
unique factorization domain In mathematics Mathematics (from Ancient Greek, Greek: ) includes the study of such topics as quantity (number theory), mathematical structure, structure (algebra), space (geometry), and calculus, change (mathematical analysis, analysis). It ...
this decomposition is unique up to the order of the factors and the multiplication of any non-unit factor by a unit (and division of the unit factor by the same unit). When the coefficients belong to integers, rational numbers or a finite field, there are algorithms to test irreducibility and to compute the factorization into irreducible polynomials (see Factorization of polynomials). These algorithms are not practicable for hand-written computation, but are available in any
computer algebra system A computer algebra system (CAS) or symbolic algebra system (SAS) is any mathematical software with the ability to manipulate mathematical expressions in a way similar to the traditional manual computations of mathematicians and scientists. The deve ...

. Eisenstein's criterion can also be used in some cases to determine irreducibility.

# Applications

## Positional notation

In modern positional numbers systems, such as the Decimal, decimal system, the digits and their positions in the representation of an integer, for example, 45, are a shorthand notation for a polynomial in the radix or base, in this case, . As another example, in radix 5, a string of digits such as 132 denotes the (decimal) number = 42. This representation is unique. Let ''b'' be a positive integer greater than 1. Then every positive integer ''a'' can be expressed uniquely in the form :$a = r_m b^m + r_ b^ + \dotsb + r_1 b + r_0,$ where ''m'' is a nonnegative integer and the ''rs are integers such that : and for .

## Interpolation and approximation

The simple structure of polynomial functions makes them quite useful in analyzing general functions using polynomial approximations. An important example in
calculus Calculus, originally called infinitesimal calculus or "the calculus of infinitesimal In mathematics, infinitesimals or infinitesimal numbers are quantities that are closer to zero than any standard real number, but are not zero. They do not ex ...
is Taylor's theorem, which roughly states that every differentiable function locally looks like a polynomial function, and the Stone–Weierstrass theorem, which states that every continuous function defined on a compact space, compact interval (mathematics), interval of the real axis can be approximated on the whole interval as closely as desired by a polynomial function. Practical methods of approximation include polynomial interpolation and the use of spline (mathematics), splines.

## Other applications

Polynomials are frequently used to encode information about some other object. The characteristic polynomial of a matrix or linear operator contains information about the operator's eigenvalues. The minimal polynomial (field theory), minimal polynomial of an algebraic element records the simplest algebraic relation satisfied by that element. The chromatic polynomial of a graph (discrete mathematics), graph counts the number of proper colourings of that graph. The term "polynomial", as an adjective, can also be used for quantities or functions that can be written in polynomial form. For example, in computational complexity theory the phrase ''polynomial time'' means that the time it takes to complete an
algorithm of an algorithm (Euclid's algorithm) for calculating the greatest common divisor (g.c.d.) of two numbers ''a'' and ''b'' in locations named A and B. The algorithm proceeds by successive subtractions in two loops: IF the test B ≥ A yields "yes" ...

is bounded by a polynomial function of some variable, such as the size of the input.

# History

Determining the roots of polynomials, or "solving algebraic equations", is among the oldest problems in mathematics. However, the elegant and practical notation we use today only developed beginning in the 15th century. Before that, equations were written out in words. For example, an algebra problem from the Chinese The Nine Chapters on the Mathematical Art, Arithmetic in Nine Sections, circa 200 BCE, begins "Three sheafs of good crop, two sheafs of mediocre crop, and one sheaf of bad crop are sold for 29 dou." We would write .

## History of the notation

The earliest known use of the equal sign is in Robert Recorde's ''The Whetstone of Witte'', 1557. The signs + for addition, − for subtraction, and the use of a letter for an unknown appear in Michael Stifel's ''Arithemetica integra'', 1544. René Descartes, in ''La géometrie'', 1637, introduced the concept of the graph of a polynomial equation. He popularized the use of letters from the beginning of the alphabet to denote constants and letters from the end of the alphabet to denote variables, as can be seen above, in the general formula for a polynomial in one variable, where the 's denote constants and denotes a variable. Descartes introduced the use of superscripts to denote exponents as well.