1. The problem statement, all variables and given/known data I have to prove: ∫(-infinity:infinity) cos(pi*v/2L)*e^-((L-L_av)^2/sqrt(2pi)*sigma^2) dL proportional to cos(pi*v/2L_av)*e^-(t/tau)^2 tau is some constant, and sigma << L_av. 3. The attempt at a solution i can change the integral to 0:infinity, since sigma << L_av. Then i have to look up some integral solution, probably: ∫(0:infinity) cos(bx)*e^-ax^2 dx I assume i have to do some trick like 1/L approximately L/L_av^2 - but how can i justify that?