1. Limited time only! Sign up for a free 30min personal tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

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.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook