1. The problem statement, all variables and given/known data A travelling wave f(x,t) = ei(kx -wt). Show that the real part of the wave can be written as cos(kx)cos(wt) + sin(kx)sin(wt) 2. Relevant equations Euler eiθ = cos(θ) + isin(θ) Also ei(θ1+θ2) = eiθ1 . eiθ2 3. The attempt at a solution The - symbol is throwing me off and I can't find any examples to help me out. Does the second equation I gave above become eiθ1 / eiθ2? And then carry on and cancel out to get the answer? Any and all help appreciated thanks.