Ax–Kochen theorem: Difference between revisions

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[[Image:Sextic Graph.svg|thumb|right|233px|Graph of a sextic function, with 5 [[critical point (mathematics)|critical points]].]]
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In [[mathematics]], a '''sextic polynomial''' is a [[polynomial]] of [[Degree of a polynomial|degree]] six.
A '''sextic equation''' or '''hexic equation''' is a [[polynomial equation]] of degree six—that is, an [[equation]] whose left hand side is a sextic polynomial and whose right hand side is zero. More precisely, it has the form:
 
:<math>ax^6+bx^5+cx^4+dx^3+ex^2+fx+g=0,\,</math>
 
where {{math|''a'' ≠ 0}} and the ''coefficients'' {{math| ''a'', ''b'', ''c'', ''d'', ''e'', ''f'', ''g''}} may either be [[integers]], [[rational number]]s, [[real number]]s, [[complex number]]s or, more generally, members of any [[field (mathematics)|field]].
 
A '''sextic function''' is a [[function (mathematics)|function]] defined by a sextic polynomial. Because they have an even degree, sextic functions appear similar to [[quartic function]]s when graphed, except they may possess an additional [[Maxima and minima|local maximum]] and local minimum each. The [[derivative]] of a sextic function is a [[quintic function]].
 
Since a sextic function is defined by a polynomial with even degree, it has the same infinite limit when the argument goes to positive or negative [[infinity]]. If the [[leading coefficient]] {{math|''a''}} is positive, then the function increases to positive infinity at both sides; and thus the function has a global minimum. Likewise, if ''a'' is negative, the sextic function decreases to negative infinity and has a global maximum.
 
==Solvable sextics==
Some sixth degree equations can be solved by factorizing into radicals, but other sextics cannot. [[Évariste Galois]] developed techniques for determining whether a given equation could be solved by radicals which gave rise to the field of [[Galois theory]].<ref name="Mathworld - Sextic Equation"/>
 
It follows from Galois theory that a sextic equation is solvable in term of radicals if and only if its [[Galois group]] is contained either in the group of order 48 which [[stabilizer (group theory)|stabilizes]] a partition of the set of the roots into three subsets of two roots or in the group of order 72 which stabilizes a partition of the set of the roots into two subsets of three roots.
 
There are formulas to test either case, and, if the equation is solvable, compute the roots in term of radicals.<ref>T. R. Hagedorn, ''General formulas for solving solvable sextic equations'', J. Algebra '''233''' (2000), 704-757</ref>
 
The general sextic equation can be solved in terms of [[Kampé de Fériet function]]s.<ref name="Mathworld - Sextic Equation">[http://mathworld.wolfram.com/SexticEquation.html Mathworld - Sextic Equation]</ref> A more restricted class of sextics can be solved in terms of [[hypergeometric functions|generalised hypergeometric functions]] in one variable using [[Felix Klein]]'s approach to solving the [[quintic equation]].<ref name="Mathworld - Sextic Equation"/>
 
==See also==
*[[Cubic function]]
*[[Septic equation]]
 
==References==
 
<references/>
 
{{Polynomials}}
 
{{DEFAULTSORT:Sextic Equation}}
[[Category:Equations]]
[[Category:Galois theory]]
[[Category:Polynomials]]
 
{{algebra-stub}}

Latest revision as of 09:46, 25 October 2014

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