1. The problem statement, all variables and given/known data In a solutions manual I read exp(i*k-a)*x=0 when x= inf. I don't see how this happens. 2. Relevant equations 3. The attempt at a solution Is there a procedure for dealing with this like l'Hospital's rule? Like if I distribute the x for exp(i*k*x-a*x) then substitute inf, and get exp(inf-inf).