Is there an identity for the cos( 1/3 x ) ?

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Discussion Overview

The discussion revolves around the existence of an identity for the cosine of one-third of an angle, specifically cos(1/3 x). Participants explore its relevance in solving cubic equations and compare it to known identities, such as the half-angle identity.

Discussion Character

  • Exploratory, Technical explanation, Conceptual clarification

Main Points Raised

  • Some participants note that while there is a half-angle identity, an identity for the third-angle cosine does not seem to exist.
  • One participant references a Wikipedia page on trigonometric identities, suggesting further exploration of the topic.
  • Another participant mentions that the identity involves complex terms, indicating a potential complexity in deriving or understanding it.
  • A later reply suggests that using an integer fraction instead of an integer could be a valid approach, hinting at broader possibilities for constructing identities.

Areas of Agreement / Disagreement

Participants do not appear to reach a consensus on the existence of a specific identity for cos(1/3 x), and multiple viewpoints regarding its complexity and potential formulations remain present.

Contextual Notes

The discussion may be limited by missing assumptions about the definitions of identities and the specific context in which they are applied, as well as unresolved mathematical steps in deriving such identities.

swampwiz
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It seems that this term comes up in solving the cubic equation. While there is the identity for the half-angle, there doesn't seem to be one for third-angle.
 
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Hi !

The identity involves complex terms :
 

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OK, I understand the general form. I didn't think to use an integer fraction in lieu of an integer. (Actually, it appears that *any* number could be used there.)
 

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