1. The problem statement, all variables and given/known data Hi , I am reading a little on introductory QM , initial chapters on waves. They have given an integral for a wavepacket , assuming at t= 0. Which is: ψ(x,0) = [itex]\int A cosk'x dk'[/itex] (I don't know how to define limits to the integral in Latex upper = k+Δk , lower limit = k-Δk) which gives ψ(x,0) = S(x)coskx , where S (x) = 2AΔK sin(Δkx)/(Δkx). 2. Relevant equations Integration by parts ? 3. The attempt at a solution Now I am totally brain stuck , it surely can't be anything complex so I should be able to do it by parts. Let u =cosk'x and dv = dk' Or am I overlooking something ?