What is the Simplified Form of This Trigonometric Identity?

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Discussion Overview

The discussion revolves around the verification of a trigonometric identity involving the sum of sine functions at specific angles. Participants are exploring the simplification of the left-hand side of the identity and examining the components involved.

Discussion Character

  • Mathematical reasoning

Main Points Raised

  • One participant presents the identity $\sin\left({A}\right)+\sin\left({A+\frac{2\pi}{3}}\right)+\sin\left({A+\frac{4\pi}{3}}\right)=0$ and begins to simplify the left-hand side.
  • Another participant requests clarification on the actual identity to be verified, indicating a need for a more explicit formulation.
  • The original poster corrects their initial post to clarify the identity being discussed.
  • A participant suggests rewriting the left-hand side as a combination of sine and cosine terms, specifically $\sin(A)\left(1+\cos\left(\frac{2\pi}{3}\right)+\cos\left(\frac{4\pi}{3}\right)\right)+\cos(A)\left(\sin\left(\frac{2\pi}{3}\right)+\sin\left(\frac{4\pi}{3}\right)\right)$.
  • Questions are raised about the values of $1+\cos\left(\frac{2\pi}{3}\right)+\cos\left(\frac{4\pi}{3}\right)$ and $\sin\left(\frac{2\pi}{3}\right)+\sin\left(\frac{4\pi}{3}\right)$, indicating a focus on evaluating these expressions.

Areas of Agreement / Disagreement

The discussion does not appear to reach a consensus, as participants are still exploring the simplification and evaluation of the identity without agreeing on a definitive outcome.

Contextual Notes

Participants have not yet resolved the specific values of the trigonometric functions involved, and there may be assumptions about the angles that are not explicitly stated.

Silver Bolt
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$\sin\left({A}\right)+\sin\left({A+\frac{2\pi}{3}}\right)+\sin\left({A+\frac{4\pi}{3}}\right)=0$

$L.H.S=\sin\left({A}\right)+\left(\sin\left({A}\right)\cos\left({\frac{2\pi}{3}}\right)+\cos\left({A}\right)\sin\left({\frac{2\pi}{3}}\right)\right)+\left(\sin\left({A}\right)\cos\left({\frac{4\pi}{3}}\right)+\cos\left({A}\right)\sin\left({\frac{4\pi}{3}}\right)\right) $

From there?
 
Last edited:
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You've only given an expression...what is the actual identity to be verified?
 
Corrected now
 
Silver Bolt said:
$\sin\left({A}\right)+\sin\left({A+\frac{2\pi}{3}}\right)+\sin\left({A+\frac{4\pi}{3}}\right)=0$

$L.H.S=\sin\left({A}\right)+\left(\sin\left({A}\right)\cos\left({\frac{2\pi}{3}}\right)+\cos\left({A}\right)\sin\left({\frac{2\pi}{3}}\right)\right)+\left(\sin\left({A}\right)\cos\left({\frac{4\pi}{3}}\right)+\cos\left({A}\right)\sin\left({\frac{4\pi}{3}}\right)\right) $

From there?

I would write the LHS as:

$$\sin(A)\left(1+\cos\left(\frac{2\pi}{3}\right)+\cos\left(\frac{4\pi}{3}\right)\right)+\cos(A)\left(\sin\left(\frac{2\pi}{3}\right)+\sin\left(\frac{4\pi}{3}\right)\right)$$

Now, what are:

$$1+\cos\left(\frac{2\pi}{3}\right)+\cos\left(\frac{4\pi}{3}\right)=?$$

$$\sin\left(\frac{2\pi}{3}\right)+\sin\left(\frac{4\pi}{3}\right)=?$$
 

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