1. The problem statement, all variables and given/known data Im stuck on a old exam in plasma physics. It is about how to determine dispersion relations for high frequency waves in cold plasma's. I'm not sure how they do in the solution manual. 2. Relevant equations B = B_0z^ E = E_0exp(i(kx-wt))z^ 3. The attempt at a solution The solution manual: http://s716.photobucket.com/user/Pitoraq/media/IMG_20170512_170136_zps0e1g7onu.jpg.html My attempt to find the solution: http://s716.photobucket.com/user/Pitoraq/media/IMG_20170512_170131_zps2f7nwaui.jpg.html My question is marked "why" in the above link. Why is S^2 - D^2 = 1 ?