[this thread was moved from the Quantum Physics subforum, hence no template] In this page : http://www.physicspages.com/2012/08/06/finite-square-barrier-scattering/ When the E<V The boundary condition tells us the equation (9) (10) and (11) (12). I tried to get the results from those equation ,but still cannot get the results like (13)(14)(15)(16)(17). I being watching a lot video about the Finite Square Barrier, they always skip the solving,only show the final results of this 4 unknown constants..... Still don't know how to solving those unknown constants like that. If any one can show me how to solving or some of the crucial step in the solving,I will really appreciate that !