# Homework Help: Waves question

1. Sep 14, 2011

### JuanYsimura

1. The problem statement, all variables and given/known data

Write a wave in one space dimension as ARe(ei(kx-wt-d))where A is the
amplitude of the wave. Find a second wave of the same frequency such that
the sum of the two vanishes at x = 0 and x = L. Assuming the wave velocity
c = w/|k| is fixed, for what frequencies ! is this possible?

3. The attempt at a solution

My attempt: I Let x1 = ARe(ei(kx-wt+d)) be wave 1 and x2 = A'Re(ei(kx-wt+d')) be wave 2.
since they vanish at x=0,L, I obtained the following equations:
ARe(ei(-wt+d))+A'Re(ei(-wt+d)) = 0 and ARe(ei(Lk-wt+d))+A'Re(ei(Lk-wt+d)) = 0.
My question is: should I solve this equations and find the frequencies that satisfy this equation ?? Am I in the right path to solve the problems? Id Like to hear different opinions and different approaches.

Thanks,

Juan

2. Sep 14, 2011

### olivermsun

You're on the right path.

Two hints:

1. Factor out everything that you can. Some factors can make 0 and others never can.
2. The fixed phase speed c and the fact that the frequency w must be the same for both waves mean there are only a couple possible choices for k'.