From Griffiths: Problem 9.4 Obtain Eq. 9.20 directly from the wave equation, by separation of variables. Eq. 9.20: f(z,t)~ = integral [-inf, inf] A~(k)e^i(kz-wt) dk where ~ denotes the complex conjugate the wave equation: f''(z) = (1/v^2) f''(t) I'm a little confused on how I can separate the variables. Can I assume that I can represent f(z,t) as A sin(kz)cos(kvt) and then calculate the aforementioned 2nd derivatives. I think my reasoning is correct but my math.... well my math isn't up to par.