 scene of different kinds of scenario that can create the phase difference distance than the other wave this is scenario number one, right now when they start there is no phase difference there is no phase difference one wave travels extra so these two waves when this point reaches here this is 2 and this is also, let's say this is 2 dash between two point of same, these are the two of which travel more distance suppose it is a destructive difference in lambda fine, constructive interference so you see the difference of two waves and if delta x is equal to 2 and plus 1 by 2 lambda is here this is 1 dash, they travel and meeting this is 2, there is 2 dash but the lower let us say this is t distance even if lambda difference is destructive difference getting it? distance suppose this would be 1 minus m2 minus 1