# Waves: When do we use $e^{i(-kx + wt)}$ as opposed to $e^{i(kx - wt)}$

1. May 24, 2014

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Both of these represent waves moving in the $+x$ direction. I have seen both used in Howard Georgi's book on waves and oscillations, but it has not been explained which is used in which circumstances. What is the difference between the two and when do we use which?