Proving Trigonometric Identities

In summary, The equation cosx - cosy=-2 sin(x + y/2) sin(x - y/2) can be simplified to (cos x sin y - sin x cos y)/2 or cos x sin y - sin x cos y without the divided by 2 part. The steps taken to reach this conclusion are not provided.
  • #1
mathnewb
3
0

Homework Statement



cosx - cosy=-2 sin(x + y/2) sin(x - y/2)


Homework Equations


dont know what identities to use


The Attempt at a Solution



ok so when i figure it out, the RHS always comes out to either...

(cos x sin y - sin x cos y)/2

or just

cos x sin y - sin x cos y without the divided by 2 part

it never equals the LHS=cosx - cosy
 
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  • #2
I asked in your previous thread https://www.physicsforums.com/showthread.php?t=309555" if you mean (x+y)/2 or x+(y/2), but you didn't answer. I also think that the rest of us here would like to see the steps you took to get to
(cos x sin y - sin x cos y)/2 or cos x sin y - sin x cos y.


01
 
Last edited by a moderator:
  • #3
i mean ((x+y)/2)
 

FAQ: Proving Trigonometric Identities

What is the purpose of proving trigonometric identities?

The purpose of proving trigonometric identities is to validate the equality of two mathematical expressions involving trigonometric functions. This is important in solving complex trigonometric equations and in applications of trigonometry in fields such as physics and engineering.

What are some common techniques used to prove trigonometric identities?

Some common techniques used to prove trigonometric identities include using algebraic manipulation, using identities of basic trigonometric functions, and converting trigonometric functions into their equivalent forms using fundamental trigonometric identities.

Can all trigonometric identities be proven?

Yes, all trigonometric identities can be proven using various techniques. However, some identities may be more difficult to prove than others and may require advanced mathematical concepts.

What are some tips for successfully proving trigonometric identities?

Some tips for successfully proving trigonometric identities include carefully reviewing the given expressions, using known trigonometric identities, breaking down complex expressions into simpler forms, and being familiar with algebraic manipulation techniques.

Are there any common mistakes to avoid when proving trigonometric identities?

Yes, some common mistakes to avoid when proving trigonometric identities include forgetting to use fundamental identities, making algebraic errors, and not simplifying expressions enough. It is also important to double check the equality of both sides of the identity before concluding the proof.

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