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Proving Trigonometric Identities

  • Thread starter mathnewb
  • Start date
  • #1
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
 

Answers and Replies

  • #2
52
0
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
3
0
i mean ((x+y)/2)
 

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