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!

Is there an identity for the cos( 1/3 x ) ?

  1. Aug 25, 2012 #1
    It seems that this term comes up in solving the cubic equation. While there is the identity for the half-angle, there doesn't seem to be one for third-angle.
  2. jcsd
  3. Aug 25, 2012 #2


    User Avatar
    Gold Member

  4. Aug 26, 2012 #3
    Hi !

    The identity involves complex terms :

    Attached Files:

    Last edited: Aug 26, 2012
  5. Aug 28, 2012 #4
    OK, I understand the general form. I didn't think to use an integer fraction in lieu of an integer. (Actually, it appears that *any* number could be used there.)
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook