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Questions in which polynomials (single or several variables) play a key role. It is typically important that this tag is combined with other tags; polynomials appear in very different contexts. Please, use at least one of the top-level tags, such as nt.number-theory, co.combinatorics, ac.commutative-algebra, in addition to it. Also, note the more specific tags for some special types of polynomials, e.g., orthogonal-polynomials, symmetric-polynomials.

56 votes
Accepted

Minimal polynomial of cos(π/n)

The minimal polynomial of $\cos(2\pi/n)$ (by William Watkins and Joel Zeitlin, The American Mathematical Monthly Vol. 100, No. 5 (May, 1993), pp. 471-474) has full clarity on this matter (just take th …
Vladimir Dotsenko's user avatar
25 votes

Relations between sums of powers

Surely there are many: these are all polynomials in one variable, so every two of them are algebraically dependent because of the transcendence degree argument :-) However, I am sure that this is not … such a combination is clearly unique - you yourself observed that they form a basis), and because of the type of symmetry it possesses, it is actually a combination of $P_1$ and $P_3$ (because other polynomials
Vladimir Dotsenko's user avatar
16 votes
Accepted

Cyclotomic polynomials.

If this were true, then you would prove that $\Phi_m(x)$ and $\Phi_n(x)$ are coprime after reduction modulo $p$, which is far from true. For instance, $\Phi_4(x)=x^2+1$ and $\Phi_2(x)=x+1$ are not cop …
Vladimir Dotsenko's user avatar
14 votes

The number of irreducible polynomials over ${\mathbb F}_p$

irreducibles uniquely, hence we have a formal power series equality $$ \frac{1}{1-qt}=\prod_{k\ge 1}\frac{1}{(1-t^k)^{M_k(q)}} $$ (indeed, the coefficient of $t^n$ on the left is the number of monic polynomials
Vladimir Dotsenko's user avatar
13 votes
Accepted

What are retracts of polynomial rings?

Existence of such an example follows from the same result of Asanuma that is crucial for Gupta's work, see the article Teruo Asanuma, "Polynomial fibre rings of algebras over noetherian rings", Inve …
Vladimir Dotsenko's user avatar
13 votes
1 answer
1k views

Irreducibility of Schur polynomials

A natural question covering both this and this question would be Let $n>2$. Describe Young diagrams $\lambda$ with at most $n$ nonempty rows (or equivalently non-increasing sequences $\lambda=(\lamb …
Vladimir Dotsenko's user avatar
11 votes

Solve this sextic

The RHS only depends on $n(n+1)$, specifically it can be written as $$ 4a\left(8(n(n+1))^3+6(n(n+1))^2+n(n+1)+\frac12\right)+4bn(n+1)+2c, $$ so you have to use the standard formulas to solve a cubic e …
Vladimir Dotsenko's user avatar
10 votes

Looking for ways how to calculate $\Phi_n(i)$

I suggest to use the following properties of cyclotomic polynomials: for $p$ prime, $k>1$, we have $\Phi_{mp^k}(x)=\Phi_{mp}(x^{p^{k-1}})$; for $p$ prime and $m$ coprime with $p$, we have $\Phi_{mp …
Vladimir Dotsenko's user avatar
10 votes

Is a polynomial with 1 very large coefficient irreducible?

Two other remarks supporting this comment: polynomials $x^n-N^n$ suggest that you should not expect anything for the constant term, and polynomials $(x^2-Nx+1)(x^2+Nx+1)=x^4+(2-N^2)x^2+1$ show that $k= …
Vladimir Dotsenko's user avatar
7 votes

Variants of Eisenstein irreducibility

A good source to learn about it is Prasolov's book on polynomials: http://tinyurl.com/prasolov - see page 53, Dumas' theorem (and a bit before this theorem). …
Vladimir Dotsenko's user avatar
6 votes
Accepted

Existence of solutions of a polynomial system

The solutions described via the link http://winvector.github.io/freq/explicitSolution.html (posted in one of the earlier answers) can be given by the following formula: $$ x_i=\frac{(k-2i)\sqrt{k}+(2 …
Vladimir Dotsenko's user avatar
5 votes

Signed factors of harmonic polynomials

. $$ For $n=3$ it looks plausible too, since Legendre polynomials appear in explicit formulas, and maybeone can play with the known fact on their roots. … Positive definiteness of polynomials is a subtle thing (cf. Hilbert's 17th problem etc.)... …
Vladimir Dotsenko's user avatar
5 votes

Is there a $3$-commutative algebra?

This variety of algebras is well studied. In particular, the description of the underlying vector space of the free algebra in this variety follows immediately from "A note on the T-ideal generated by …
Vladimir Dotsenko's user avatar
5 votes

Is there a $3$-commutative algebra?

I have just thought of another interesting example, which is a bit peculiar, in that the 3-commutativity property arises for a natural subspace of an algebra which itself does not satisfy any identity …
Vladimir Dotsenko's user avatar
4 votes

Degree of sum of algebraic numbers

Irreducibles and the composed product for polynomials over a finite field. MR0893074 (89g:11118)). …
Vladimir Dotsenko's user avatar

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