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Hello at physics lectures we wrote a phase of a sine wave like this:

$$\phi = kx - \omega t$$

Is this right? As I recall the phase of a wave should be written like this:

$$\phi = \omega t - kx$$

And if a wave changes direction $(k \rightarrow -k)$ like this:

$$\phi = \omega t + kx$$

Can someone explain to me if first usage is even possible and when if so.

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The first two phases are the same, the sine only differs by an overall sign i.e. by normalization. The last formula only differs by its being a left-moving wave rather than a right-moving wave, i.e. by the sign of $k$. –  Luboš Motl Sep 25 '12 at 12:16
    
Soo it holds that $\sin(x) = - \sin(-x)$ and therefore $\sin(\omega t - kx) = - \sin(kx - \omega t)$? –  71GA Sep 25 '12 at 19:00
    
Could you post your anwser below so i can give you points? –  71GA Oct 21 '12 at 7:07
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up vote 0 down vote accepted

It holds that $\sin(x) = - \sin(-x)$ and therefore $\sin(\omega t - kx) = - \sin(kx - \omega t)$.

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