We've been looking at the Forurier series in our lectures which has been fine and it's okay for heat transfer, but we covered the wave eqt today and I've been left baffled. Using the boundary conditions of he diaplacement at each end of the string to be 0, we got the genral eqt y(x,t) = [Ccos (nctpi/L) + Dsin(nctpi/L)]sin(nxpi/L) However, in the final solution, there is no cosine term, (even though C exists and D is zero). Where did it go to? Can someone please give me a quick run-down on this because I'm just baffled right now. In the final eqt we mulitply C by sin(nctpi/L)sin(nxpi/c) I get how to calculate the C term okay. It's just the diappearence of the cosine term that has me confused. The question that we're given for our homework is the same as there's no cosine term in that answer either. What am I doing wrong?