Talk:Complex conjugate root theorem

generalization?

maybe one could mention that the same theorem applies to an analytic function whose series has real coefficients (but the result is restricted to the part of the domain where the series represents the function). Lunch 21:20, 30 January 2007 (UTC)

comment from the AfD

there was a comment on the AfD that caught my eye:

Keep. In the future, this page could maybe be renamed into "Properties of polynomial roots". (This would solve the google test and the somewhat clumsy name. See above comment by ais523.) In addition to the complex conjugate property, such a page could also disucss: 1) how roots depend continuously but not differentiably on the coefficients, 2) bounds on the roots in terms of the coefficients. There are probably many other properties of polynomials that merit a discussion. Haseldon 18:55, 30 January 2007 (UTC)

one could also throw in such trivia as: the convex hull of the roots of a polynomial contains the roots of the derivative of the polynomial. (with the corollary that if a polynomial's roots all have positive real part, then so do the roots of all its derivatives.)

cheers, Lunch 17:27, 31 January 2007 (UTC)

As a start I created Properties of polynomial roots. There is still lots of work though. Haseldon 19:33, 31 January 2007 (UTC)

Quick proof

Can someone find a source for the easy proof of the corollary on odd degrees:

• Since complex roots come in conjugate pairs, there are an even number of them;
• But a polynomial of odd degree has an odd number of roots;
• So some of them must be non-complex, and so real.

This requires some care in the presence of multiple roots; but WP is an encyclopedia, not a textbook; we can simply say that. Septentrionalis PMAnderson 20:07, 31 January 2007 (UTC)

Fundamental theorem of algebra care

The article states that the fundamental theorem of algebra can be used to imply that an odd polynomial must have a real root. However, the proofs that I've seen of the fundamental theorem of algebra use the fact that odd polynomials have a real root. Hence there is circular reasoning here: one should not use a theorem to deduce a lemma that is required to prove the theorem. I know it also says IVT, but I believe this should be the only thing, or if the fundamental theorem is mentioned, it should be with a caveat (or better, note that this fact is used in proving the fundamental theorem). asmeurer (talk | contribs) 00:09, 24 February 2018 (UTC)