v 7.2

ω [t - \frac{z^{″} n}{c} - (z - z^{″}) \frac{n}{c}] = ω [t - z \frac{n}{c}]

${\omega \bigg[t- \frac{z'' n}{c} - (z-z'') \frac{n}{c}\bigg]=\omega \bigg[t-z \frac{n}{c} \bigg]}$

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