Two spherical waves with the same amplitude, A, and wavelength, ?, are spreading out from two point sources S1 and S2 along one side of a barrier. The two waves have the same phase at positions S1 and S2. The two waves are superimposed at a position P. If the two waves interfere constructively at P what is the relationship between the path length difference dx=d2-d1 and the wavelength. If the two waves interfere destructively at P, what is the relationship between the path length difference and the wavelength?