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Deduction in Trigonometric

  1. Jun 20, 2007 #1
    Anybody that can show how to deduce
    cos(a+b) = cos(a)cos(b) - sin(a)sin(b)
    sin(a+b) = sin(a)cos(b) + sin(b)cos(a)
    From the relations that we get from eulers formula..
    Should be really simple but I think that I have got some relations wrong so I need to se the real solution.:uhh:
  2. jcsd
  3. Jun 20, 2007 #2
    Which relations have you got wrong?
  4. Jun 20, 2007 #3
    Your relations are fine. Use this to verify it:

    [tex]cos(a + b) = Re[cis(a)cis(b)][/tex]
    [tex]sin(a + b) = Im[cis(a)cis(b)][/tex]
  5. Jun 20, 2007 #4
    Hehe it turned out to be that I had it all right I had just made a stupid misstake and was to close to detect it.
    Thanks for the help, both of you.
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