What does the product of two cosine functions represent in terms of angles?

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Discussion Overview

The discussion revolves around the interpretation of the product of two cosine functions, specifically \(\cos \theta_1 \cos \theta_2\), in relation to angles. Participants explore its geometric meaning, potential connections to the dot product, and the implications of trigonometric identities.

Discussion Character

  • Exploratory
  • Conceptual clarification
  • Debate/contested
  • Mathematical reasoning

Main Points Raised

  • One participant questions whether \(\cos \theta_1 \cos \theta_2\) represents a dot product and expresses uncertainty about its meaning.
  • Another participant suggests that the interpretation depends on the context of the angles involved, particularly what vectors they may relate to.
  • A geometrical interpretation is proposed, indicating that if angles \(\theta_1\) and \(\theta_2\) are contiguous at the same vertex, the product represents how a segment shrinks upon successive perpendicular projections through those angles.
  • One participant acknowledges the ambiguity of the question and refers to a previous thread for further context.
  • A participant provides a trigonometric identity that transforms the product into a sum of cosines, indicating that the product itself may not have intrinsic meaning beyond this transformation.
  • Another participant admits to initially overlooking trigonometric identities and expresses gratitude for the clarification received.

Areas of Agreement / Disagreement

Participants express varying degrees of uncertainty regarding the interpretation of the cosine product, with no consensus reached on its meaning. Some propose interpretations while others highlight the ambiguity of the question.

Contextual Notes

The discussion reflects limitations in assumptions about the context of the angles and the specific mathematical framework being applied. The interpretations presented depend on the definitions and situations described by participants.

trancefishy
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what exactly does [tex]\cos \theta_1 \cos \theta_2[/tex] represent, in relation to the angles? is this a dot product? i have played, and don't really see what this product is supposed to represent.

EDIT: you know, i may have just answered my own question with a mere trig identity... perhaps i will figure this thing out I'm working on pretty soon...
 
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It would depend upon where these angles came from (dot product of what vectors?).

Imagine I asked why x^2 represented - a slightly ambiguous question, isn't it?
 
A simple geometrical interpretation I can think of: if you angles t1 and t2 are contiguous, and at the same vertex, the factor cos(t1)cos(t2) is the factor that a segment would shrink upon succesive perpendicular projections through those angles.

But, as Matt says, it would be useful to know more about the particular situation in which you are trying to interpret the product.
 
trancefishy said:
yes, i'd imagine it is a bit more ambiguous than I had supposed... I'm working on this
https://www.physicsforums.com/showthread.php?t=57665

You refer to my post??What is ambiguous about that??It's true i didn't make any picture,but i relied upon your imagination.I guess u're all to familiar with spherical coordinates and the angles [itex]\theta[/itex] and [itex]\phi[/itex].Else,it's just math.A bit of ingenuity,though,else the geometric-triginomotric approach would have been more difficult to understand and would have necessitated a drawing.
That is just a simple product of trigonometrical functions.It has no meaning other than the one specified already.If u don't like that product (though i still cannot imagine the reasons),u can use this formula to transform it into a sum of cosines:
[tex]\cos \alpha \cos \beta=\frac{1}{2}[\cos(\alpha+\beta)+\cos(\alpha-\beta)][/tex]

I sincerely hope u're giving your best shot...Math is not a domain in which being lazy gives results...

Daniel.
 
that's what i missed. i (embarrassingly) just didn't think of trig identities. btw, i posted this thread before you had replied to my problem. i do thank you for your well given response, all is understood now :-)
 
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