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Can't make sense of this trig identity

  1. Sep 10, 2008 #1
    1. The problem statement, all variables and given/known data
    im in first year differential calculas and i have no idea what my prof wrote down...i just copied it and thought ide figure it out later. but i cant fore the life of me.


    2. Relevant equations
    the identitie that he wrote is:

    sinC+sinB=2Sin (C+D)/2 cos (c-D)/2


    3. The attempt at a solution
     
  2. jcsd
  3. Sep 10, 2008 #2
    Re: identities!!!!

    side note ) x+y = c
    x-y = b
     
  4. Sep 10, 2008 #3
    Re: identities!!!!

    i understand where the sin C + sin B, its the (c+d)/2 that has me confused.........these identities are just another way of writing the identities derived from adding and subtracting the addition and subtraction identities
     
  5. Sep 10, 2008 #4

    Dick

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    Re: identities!!!!

    Change the 'D' to 'B'. Then it works. Sure, it's derived from addition and subtraction identities. Basically everything is.
     
  6. Sep 10, 2008 #5
    Re: identities!!!!

    where did the (c+b)/2 come from.......i know they subbed that in for x....but why?
     
  7. Sep 10, 2008 #6

    Dick

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    Re: identities!!!!

    I don't know, you didn't give us the whole problem. I do know sin(c)+sin(b)=2*sin((c+b)/2)*cos((c-b)/2).
     
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