Since the point x = 0 is a node and reflection is taking place from point x = 0. This means that reflection must be taking place from the fixed end and hence the reflected ray must suffer an additional phase change of π or a path change of
λ
2
. So, if yincident =acos(kx−ωt) ⇒yincident =acos(−kx−ωt+π) =−acos(ωt+kx) Hence equation for the other wave y=acos(kx+ωt+π)